Intel Core i5-2500K vs Intel Core i5-6400 Comparison

The Verdict

The data is unambiguous. Across every recorded benchmark in the database, the Intel Core i5-6400 defeats the Intel Core i5-2500K. The i5-6400 wins all seven head-to-head comparisons, with no single test favoring the older Sandy Bridge part. For any user selecting strictly on measured performance, the i5-6400 is the correct choice.

The i5-6400 leads by modest margins in Cinebench workloads. In Cinebench R15 multicore, it scores 364 against 354 for the i5-2500K, a 2.7% advantage. In Cinebench R23 multicore, it scores 3614 versus 3523, a 2.5% edge. Single-core Cinebench results follow the same pattern: R20 single-core shows 214 versus 208 (2.8% ahead), and R23 single-core shows 510 versus 497 (2.5% ahead). These are narrow wins, but they are consistent across every iteration of the Cinebench test.

The Geekbench results tell a different story in magnitude. The i5-6400 scores 3134 in Geekbench multicore, which is 22.3% higher than the 2434 posted by the i5-2500K. In Geekbench single-core, the i5-6400 scores 1048 against 805, a 23.2% advantage. This is the largest gap between the two processors in any test, and it indicates the Skylake architecture delivers substantially better performance per clock in workloads that resemble Geekbench's mix.

Both processors sit at the 35th percentile among all CPUs in the database, meaning they land in the same overall performance tier despite the i5-6400's consistent wins. The average benchmark score tells a similar story: the i5-2500K averages 1329 points, while the i5-6400 averages 1307 points. The i5-6400's average is actually 1.7% lower despite winning every head-to-head test, which reflects differences in the benchmark set used to compute the average. The nearest rivals for each processor reinforce this closeness: the i5-2500K sits within 0.6% of the Intel Celeron G6900T and G6900E, while the i5-6400 sits within 0.8% of the Intel Core i7-3610QE.

Who should pick which? A user who needs the highest measured scores in the database, particularly in Geekbench, should choose the i5-6400. A user who requires an unlocked multiplier for overclocking has only one option in this comparison, since the i5-2500K has an unlocked multiplier while the i5-6400 does not. That feature is not reflected in the stock benchmark scores, but it is a functional difference that matters for a specific audience. For everyone else, the recorded data favors the i5-6400.

FAQ

Q: Which processor wins the most benchmarks?

A: The Intel Core i5-6400 wins all seven head-to-head benchmark comparisons in the database. The i5-2500K does not win a single test.

Q: How large is the performance gap in Geekbench?

A: The i5-6400 leads by 22.3% in Geekbench multicore (3134 versus 2434) and by 23.2% in Geekbench single-core (1048 versus 805). These are the largest margins recorded between the two processors.

Q: Are the Cinebench differences large or small?

A: They are small. The i5-6400 leads by 2.7% in Cinebench R15 multicore, 2.5% in R20 multicore, 2.8% in R20 single-core, 2.5% in R23 multicore, and 2.5% in R23 single-core. Every Cinebench result falls in a narrow range between 2.5% and 2.8%.

Q: Do both processors have the same number of cores and threads?

A: Yes. Both the Intel Core i5-2500K and the Intel Core i5-6400 have 4 cores and 4 threads. Neither processor supports simultaneous multithreading.

Q: Which processor has a higher base clock?

A: The Intel Core i5-2500K has a base clock of 3.30 GHz, which is higher than the 2.70 GHz base clock of the Intel Core i5-6400. The i5-2500K also has a higher boost clock at 3.70 GHz versus 3.30 GHz.

Q: Can both processors be overclocked?

A: No. The Intel Core i5-2500K has an unlocked multiplier, so it can be overclocked. The Intel Core i5-6400 has a locked multiplier, so it cannot be overclocked through the multiplier.

Architecture Differences

The two processors come from different architectural generations. The Intel Core i5-2500K is based on Sandy Bridge, while the Intel Core i5-6400 is based on Skylake. The manufacturing process differs accordingly: the i5-2500K uses a 32 nm node, while the i5-6400 uses a 14 nm node. Both are fabricated by Intel, but the die sizes differ. The i5-2500K has a die size of 216 mm², while the i5-6400 is smaller at 177 mm². The transistor count for the i5-2500K is listed at 1,160 million, while no transistor count is recorded for the i5-6400.

Cache organization is identical in structure. Both processors feature 64 KB of L1 cache per core and 256 KB of L2 cache per core. L3 cache is 6 MB shared on both parts. The cache hierarchy itself did not change between these two generations, but the underlying architecture did, which explains why the i5-6400 achieves higher scores despite lower clock speeds.

The integrated graphics differ. The i5-2500K includes Intel HD 3000, while the i5-6400 includes HD Graphics 530. The memory controller also changed. The i5-2500K supports DDR3 memory, while the i5-6400 supports DDR4 memory. Both use dual-channel memory buses, but the peak memory bandwidth differs: the i5-2500K reaches 25.6 GB/s, while the i5-6400 reaches 34.1 GB/s. That bandwidth advantage likely contributes to the i5-6400's larger Geekbench wins.

PCI Express support is another generation-specific difference. The i5-2500K provides PCIe Gen 2 with 16 lanes from the CPU, while the i5-6400 provides PCIe Gen 3 with 16 lanes from the CPU. The newer PCIe standard on the i5-6400 offers higher bandwidth to attached devices, though the recorded benchmarks in the database are CPU-focused.

The sockets are incompatible. The i5-2500K uses Intel Socket 1155, while the i5-6400 uses Intel Socket 1151. A motherboard designed for one will not accept the other. The market segment for both is Desktop, and both processors are end-of-life in production status.

The i5-2500K was released earlier, with a release date of 2011-01-08, and the i5-6400 followed with a release date of 2015-07-01. The i5-2500K launch MSRP was $216, and the i5-6400 launch MSRP was $182. The part numbers are SR008 for the i5-2500K and SR2L7 for the i5-6400.

Specification Differences

The core count and thread count are the same: 4 cores and 4 threads for both processors. The base clock differs, with the i5-2500K at 3.30 GHz and the i5-6400 at 2.70 GHz. The boost clock also differs, with the i5-2500K at 3.70 GHz and the i5-6400 at 3.30 GHz. Despite the clock disadvantage, the i5-6400 wins every benchmark.

Thermal design power differs substantially. The i5-2500K has a TDP of 95 watts, while the i5-6400 has a TDP of 65 watts. The i5-6400 delivers higher performance at a lower power envelope, a direct result of the 14 nm manufacturing process.

The architecture and codename differ: Sandy Bridge for the i5-2500K and Skylake for the i5-6400. The generation labels follow the architecture names. The process node differs as noted, 32 nm versus 14 nm. The die size differs, 216 mm² versus 177 mm². The transistor count is recorded only for the i5-2500K at 1,160 million.

Memory support differs by generation. The i5-2500K supports DDR3, while the i5-6400 supports DDR4. Both use a dual-channel memory bus, but memory bandwidth is higher on the i5-6400 at 34.1 GB/s versus 25.6 GB/s. Neither processor supports ECC memory.

PCIe support differs. The i5-2500K provides Gen 2 with 16 lanes, while the i5-6400 provides Gen 3 with 16 lanes. The integrated graphics differ, with Intel HD 3000 on the i5-2500K and HD Graphics 530 on the i5-6400.

The socket differs, 1155 versus 1151. The multiplier unlock status differs: the i5-2500K has an unlocked multiplier, and the i5-6400 does not. Release dates differ, and launch MSRP differs, with the i5-2500K at $216 and the i5-6400 at $182. The part numbers differ as well.

Head-to-Head Benchmarks

The most decisive results come from Geekbench. In Geekbench multicore, the i5-6400 scores 3134 against 2434 for the i5-2500K, a 22.3% advantage. In Geekbench single-core, the i5-6400 scores 1048 against 805, a 23.2% advantage. These are the two largest deltas in the entire comparison. The Geekbench suite appears to reward the Skylake architecture's improvements more heavily than Cinebench does, and the higher memory bandwidth of the i5-6400 may also play a role.

The Cinebench results are tighter but still consistently favor the i5-6400. In Cinebench R15 multicore, the i5-6400 scores 364 versus 354, a 2.7% lead. In Cinebench R20 multicore, it scores 1517 versus 1479, a 2.5% lead. In Cinebench R23 multicore, it scores 3614 versus 3523, a 2.5% lead. The single-core Cinebench results follow the same pattern: R20 single-core shows 214 versus 208 (2.8%), and R23 single-core shows 510 versus 497 (2.5%).

The i5-2500K has no wins in any recorded test. Its higher base and boost clocks do not translate into benchmark victories. The i5-6400 compensates for its lower clocks with architectural efficiency, a smaller manufacturing process, and a faster memory interface. The data shows that clock speed alone does not determine performance in these workloads.

The average benchmark scores in the database present an interesting nuance. The i5-2500K averages 1329 points, while the i5-6400 averages 1307 points. The i5-2500K's nearest rivals include the Intel Core i5-4460S at 1330 points (0.1% ahead) and the Intel Core i5-760 at 1337 points (0.6% ahead). The i5-6400's nearest rivals include the Intel Core i7-3770T at 1314 points (0.5% ahead) and the AMD Athlon Gold 7220U at 1311 points (0.3% ahead). The two processors occupy the same performance tier in the database, even though the direct head-to-head benchmarks all favor the i5-6400.

For a buyer looking at raw benchmark results, the choice is clear. The i5-6400 outperforms the i5-2500K in every recorded test, with the largest margins appearing in Geekbench. The only reason to select the i5-2500K is the unlocked multiplier, which enables overclocking that the locked i5-6400 cannot offer. The stock data, however, belongs entirely to the i5-6400.