Intel Core i5-6600 vs Intel Core i7-990X Comparison

Where Each One Wins

The benchmark split between these two processors is unusually stark. The Intel Core i5-6600 claims victory in exactly two tests, both from the Geekbench suite. The Intel Core i7-990X takes the remaining six, sweeping every Cinebench iteration. This is not a case of one chip being broadly superior; it is a case of two very different workloads favoring two very different designs.

The i5-6600 wins decisively in Geekbench single-core with a score of 1239 against 556, a margin of 122.8%. It also leads in Geekbench multicore at 3755 versus 2612, a 43.8% advantage. These are synthetic workloads that heavily reward newer instruction sets, memory latency characteristics, and per-core efficiency. The data suggests the i5-6600 is the better choice for tasks that are latency-sensitive or lightly threaded, where raw core count matters less than how fast each individual core can execute.

The i7-990X dominates every Cinebench result. In Cinebench R23 multicore, it scores 6071 against 5161, a 15% lead. The pattern repeats in R20 (2549 vs 2167), R15 (611 vs 520), and all single-core variants as well. Cinebench is a rendering workload that scales with core count and thread count, so the 6-core, 12-thread i7-990X naturally outpaces the 4-core, 4-thread i5-6600. But even in Cinebench single-core tests, the older i7-990X wins by 15.1% in R23 (857 vs 728). This indicates that the i7-990X's higher base clock of 3.47 GHz and its Westmere architecture are not simply obsolete; they still deliver competitive per-thread rendering performance.

The use-case split is clear. The i5-6600 is the pick for general desktop responsiveness, older software, and Geekbench-style workloads that favor modern IPC and memory architecture. The i7-990X is the pick for multi-threaded rendering and productivity tasks where its 12 threads provide a consistent advantage.

Architecture Differences

The two chips come from different eras of Intel's design philosophy. The i5-6600 is built on the Skylake architecture, produced on a 14 nm process with a die size of 177 mm². The i7-990X uses the older Westmere architecture, codenamed Gulftown, on a 32 nm process with a much larger die at 239 mm² and 1,170 million transistors. The process node difference is significant: 14 nm versus 32 nm is a generational leap in manufacturing efficiency.

Core configuration is the most obvious divergence. The i5-6600 has 4 cores and 4 threads, while the i7-990X has 6 cores and 12 threads thanks to Hyper-Threading. This explains the Cinebench multicore results. Cache hierarchies also differ. Both share 64 KB L1 and 256 KB L2 per core, but the L3 cache jumps from 6 MB shared on the i5-6600 to 12 MB shared on the i7-990X. That extra cache likely helps the older chip in rendering workloads.

Memory support is another split. The i5-6600 supports DDR3 and DDR4 with dual-channel memory and a bandwidth of 34.1 GB/s. The i7-990X supports only DDR3 but uses a triple-channel memory bus. The i5-6600's memory bandwidth figure is recorded at 34.1 GB/s, while the i7-990X has no listed bandwidth figure, but triple-channel DDR3 was a high-bandwidth design for its time.

PCIe capabilities differ as well. The i5-6600 has PCIe Gen 3 with 16 lanes (CPU only), while the i7-990X has PCIe Gen 2. Integrated graphics also separate them: the i5-6600 includes UHD Graphics 530, while the i7-990X has none. The i5-6600's TDP is 35 watts, a remarkably low figure compared to the i7-990X's 130 watts. The i7-990X also has an unlocked multiplier, whereas the i5-6600 is locked. Sockets are incompatible: Socket 1151 for the i5-6600, Socket 1366 for the i7-990X.

Head-to-Head Benchmarks

The most dramatic result is Geekbench single-core. The i5-6600 scores 1239, the i7-990X scores 556. That is a 122.8% advantage, meaning the i5-6600 more than doubles the older chip's per-core performance in this specific test. This is a massive gap, far larger than any Cinebench margin. It reflects the modern Skylake core's ability to execute instructions more efficiently per clock, plus its newer memory subsystem.

Geekbench multicore also favors the i5-6600, but by a smaller margin: 3755 versus 2612, a 43.8% lead. Even with only 4 threads, the i5-6600 outruns the 12-thread i7-990X in this benchmark. This suggests Geekbench's multicore test does not scale purely with thread count; it rewards per-core speed and memory bandwidth in ways that favor the newer architecture.

Cinebench tells the opposite story. The i7-990X wins R15 multicore with 611 against 520, a 14.9% lead. R20 multicore shows 2549 versus 2167, a 15% lead. R23 multicore shows 6071 versus 5161, also a 15% lead. The consistency across all three Cinebench versions is striking: the i7-990X is always roughly 15% ahead in multicore rendering.

Single-core Cinebench results are less expected. The i7-990X wins R15 single-core with 86 versus 73, a 15.1% lead. R20 single-core: 359 versus 305, a 15% lead. R23 single-core: 857 versus 728, a 15.1% lead. Despite the i5-6600's massive Geekbench single-core win, the i7-990X wins every Cinebench single-core test by about 15%. This divergence likely stems from how each benchmark measures performance: Geekbench favors the Skylake's modern instruction handling, while Cinebench's rendering engine rewards the i7-990X's higher base clock (3.47 GHz vs 3.30 GHz) and its specific cache hierarchy.

The overall win count is 6 for the i7-990X and 2 for the i5-6600. But the average benchmark scores tell a closer story: the i5-6600 averages 1744, the i7-990X averages 1713. The i5-6600 sits at the 41st percentile of all CPUs, the i7-990X at the 40th. These are nearly identical overall performance tiers, despite very different strengths.

FAQ

Q: Which processor has more cores and threads?

A: The Intel Core i7-990X has 6 cores and 12 threads. The Intel Core i5-6600 has 4 cores and 4 threads.

Q: Why does the i7-990X win all Cinebench tests but lose Geekbench?

A: Cinebench is a rendering workload that scales with thread count and raw clock speed. The i7-990X has 12 threads and a 3.47 GHz base clock, giving it a consistent 15% lead in Cinebench. Geekbench rewards per-core efficiency and modern memory architecture, where the Skylake-based i5-6600 excels, leading to a 122.8% single-core advantage.

Q: What is the TDP difference between these two chips?

A: The i5-6600 has a TDP of 35 watts. The i7-990X has a TDP of 130 watts. The i5-6600 draws significantly less power despite being the newer design.

Q: Do both processors support integrated graphics?

A: No. The i5-6600 includes UHD Graphics 530. The i7-990X has no integrated graphics, so it requires a discrete GPU.

Q: Are these processors overclockable?

A: The i7-990X has an unlocked multiplier, meaning it can be overclocked. The i5-6600 has a locked multiplier, so it cannot be overclocked by conventional means.

Q: Which chip has a higher average benchmark score?

A: The i5-6600 has an average benchmark score of 1744. The i7-990X has an average score of 1713. The difference is small, roughly 1.8%, and the percentile rankings are nearly identical at 41 and 40.

Specification Differences

The two processors differ in nearly every major specification category.

• Cores: 4 (i5-6600) vs 6 (i7-990X)
• Threads: 4 (i5-6600) vs 12 (i7-990X)
• Base clock: 3.30 GHz (i5-6600) vs 3.47 GHz (i7-990X)
• Boost clock: 3.90 GHz (i5-6600) vs 3.73 GHz (i7-990X)
• TDP: 35 W (i5-6600) vs 130 W (i7-990X)
• Socket: Intel Socket 1151 (i5-6600) vs Intel Socket 1366 (i7-990X)
• Process node: 14 nm (i5-6600) vs 32 nm (i7-990X)
• Die size: 177 mm² (i5-6600) vs 239 mm² (i7-990X)
• Transistors: not listed (i5-6600) vs 1,170 million (i7-990X)
• L3 cache: 6 MB shared (i5-6600) vs 12 MB shared (i7-990X)
• Memory support: DDR3, DDR4 (i5-6600) vs DDR3 only (i7-990X)
• Memory bus: Dual-channel (i5-6600) vs Triple-channel (i7-990X)
• PCIe: Gen 3, 16 Lanes (i5-6600) vs Gen 2 (i7-990X)
• Integrated graphics: UHD Graphics 530 (i5-6600) vs none (i7-990X)
• Multiplier unlocked: No (i5-6600) vs Yes (i7-990X)

The Verdict

The data presents a clear choice based on workload, not a universal winner. For users running Geekbench-style applications, general desktop tasks, or software that benefits from modern memory bandwidth (34.1 GB/s on the i5-6600) and per-core speed, the Intel Core i5-6600 is the superior processor. Its 122.8% single-core Geekbench lead is enormous, and even its multicore Geekbench score is 43.8% higher despite having one-third the threads.

For rendering workloads represented by Cinebench, the Intel Core i7-990X is the stronger pick. It wins every Cinebench test by about 15%, thanks to its 6 cores, 12 threads, and 12 MB of L3 cache. Its higher base clock of 3.47 GHz also contributes to single-core Cinebench wins, which is surprising given the i5-6600's newer architecture.

The average benchmark scores are nearly tied at 1744 versus 1713, placing both at the 40th and 41st percentiles respectively. Neither chip is a dominant overall performer by this metric. The choice comes down to whether the user prioritizes the i5-6600's modern efficiency (35 W TDP, integrated graphics, PCIe Gen 3) or the i7-990X's raw thread count and cache capacity (130 W TDP, no iGPU, PCIe Gen 2).

The i7-990X also offers an unlocked multiplier for overclocking, while the i5-6600 does not. The i5-6600 has the advantage of DDR4 memory support and a much lower power draw. The i7-990X has triple-channel memory and a larger die. The data does not point to one chip being universally better; it points to two specialized tools for different jobs. The i5-6600 is for modern, latency-sensitive, power-conscious systems. The i7-990X is for multi-threaded rendering where every extra thread counts.