Intel Core i3-8350K vs Intel Core i5-8259U Comparison

The Intel Core i5-8259U and the Intel Core i3-8350K are both 14 nm Coffee Lake parts, but they target opposite ends of the computing spectrum: one is a mobile processor, the other a desktop chip. The benchmark data shows a clear split, with the mobile i5-8259U dominating CPU-rendering workloads while the desktop i3-8350K takes a decisive lead in system-level Geekbench tests. The average benchmark scores are nearly identical, at 2108 for the i5-8259U and 2096 for the i3-8350K, placing both at the 46th percentile of all CPUs.

Head-to-Head Benchmarks

The Cinebench suite is a total sweep for the Intel Core i5-8259U. In Cinebench R15 multi-core, the i5-8259U scores 667 against 593 for the i3-8350K, a 12.5% advantage. The single-core R15 test shows an even larger gap: 94 versus 83, a 13.3% win. That pattern holds across every Cinebench version in the data. In R20, the i5-8259U posts 2781 multi-core and 392 single-core, versus 2471 and 348 for the i3-8350K, representing 12.5% and 12.6% leads respectively. The R23 results are consistent: 6622 multi-core versus 5884, and 934 single-core versus 830, both again a 12.5% difference. The consistency of these deltas across all three Cinebench versions suggests a fundamental architectural advantage rather than a workload-specific quirk.

The story flips completely in Geekbench. Here, the Intel Core i3-8350K wins multi-core with 4992 versus 4168 for the i5-8259U, a 16.5% margin. The single-core Geekbench result is even more lopsided, with the i3-8350K scoring 1564 against 1207, a 22.8% advantage. This is a substantial reversal. The i5-8259U wins 6 of the 8 head-to-head benchmarks, but the two Geekbench losses are by far the largest margins in either direction. The i3-8350K’s Geekbench wins are not narrow; they are decisive, dwarfing the i5-8259U’s consistent but smaller Cinebench leads.

Where Each One Wins

The Intel Core i5-8259U wins in every Cinebench test, which exercises sustained multi-threaded and single-threaded rendering workloads. Its lead is uniform, hovering around 12.5% across multi-core and single-core tests alike. This indicates that the i5-8259U is the stronger choice for applications that rely on the Cinebench rendering engine or similar CPU-bound content-creation tasks. The i5-8259U’s 8 threads, compared to the i3-8350K’s 4, likely contribute to its multi-core edge, but the single-core lead shows it is not merely a thread-count advantage.

The Intel Core i3-8350K wins in Geekbench, which measures a broader mix of real-world tasks including encryption, image processing, and memory operations. Its 16.5% multi-core and 22.8% single-core leads are substantial, suggesting better raw performance in everyday computing and desktop productivity scenarios. The i3-8350K’s higher base clock of 4.00 GHz, compared to the i5-8259U’s 2.30 GHz base, is a likely factor. The i5-8259U does have a 3.80 GHz boost clock, but the i3-8350K has no boost clock listed, meaning it runs at its full 4.00 GHz at all times, which could explain its Geekbench dominance.

Architecture Differences

Both CPUs share the Coffee Lake architecture and are built on Intel’s 14 nm process node. They also share the same die size of 126 mm². The fundamental difference is in their target platforms: the i5-8259U uses the Coffee Lake-U codename and is designed for mobile, while the i3-8350K uses the standard Coffee Lake codename and is a desktop part. This is reflected in their sockets, with the i5-8259U using Intel BGA 1526 and the i3-8350K using Intel Socket 1151.

The core configurations are a key differentiator. The i5-8259U has 4 cores and 8 threads, meaning it supports Hyper-Threading. The i3-8350K also has 4 cores but only 4 threads, no Hyper-Threading. The L3 cache differs, with the i5-8259U having 6 MB shared and the i3-8350K having 8 MB shared. Both have identical L1 and L2 caches at 64 KB and 256 KB per core respectively. The integrated graphics also differ: the i5-8259U features Iris Pro Plus 655, while the i3-8350K has UHD Graphics 630. The i5-8259U is not multiplier-unlocked, whereas the i3-8350K is, giving the desktop chip overclocking headroom.

Specification Differences

The most obvious specification difference is TDP. The i5-8259U is rated at 28 W, while the i3-8350K is rated at 91 W. This is a direct consequence of their target markets: mobile versus desktop. Clock speeds also differ significantly. The i5-8259U has a 2.30 GHz base clock and a 3.80 GHz boost clock. The i3-8350K has a 4.00 GHz base clock and no listed boost clock, meaning it operates at a fixed 4.00 GHz.

Memory support is identical in type and bus: both support DDR4 on a dual-channel bus with 38.4 GB/s bandwidth. However, ECC memory support differs: the i5-8259U does not support ECC, while the i3-8350K does. PCIe configuration is the same, with Gen 3 and 16 lanes from the CPU. The release dates are different, with the i3-8350K launching on 2017-10-04 and the i5-8259U on 2018-04-04. Both are end-of-life products. The launch MSRP for the i5-8259U is $320, and for the i3-8350K it is $168. The market segments are Mobile and Desktop, respectively.

FAQ

Q: Which CPU has the higher average benchmark score?

A: The Intel Core i5-8259U has an average benchmark score of 2108, slightly ahead of the Intel Core i3-8350K’s 2096, a delta of 0.6%.

Q: How do the two CPUs compare in Cinebench R23 multi-core?

A: The Intel Core i5-8259U scores 6622, which is 12.5% higher than the Intel Core i3-8350K’s 5884.

Q: What is the biggest performance gap in either direction?

A: The largest margin is in Geekbench single-core, where the Intel Core i3-8350K leads by 22.8%, scoring 1564 versus 1207 for the i5-8259U.

Q: Do both CPUs have the same number of threads?

A: No. The Intel Core i5-8259U has 8 threads, while the Intel Core i3-8350K has 4 threads, despite both having 4 physical cores.

Q: Which CPU supports ECC memory?

A: The Intel Core i3-8350K supports ECC memory, while the Intel Core i5-8259U does not.

Q: Are both CPUs built on the same manufacturing process?

A: Yes, both the Intel Core i5-8259U and the Intel Core i3-8350K are built on Intel’s 14 nm process node.

The Verdict

The data presents two distinct profiles. The Intel Core i5-8259U is the clear winner for rendering workloads, as evidenced by its consistent 12.5% lead across all Cinebench versions. Its 8 threads and Iris Pro Plus 655 graphics make it a capable mobile processor for content creation on the go, despite its lower base clock. The i3-8350K, with its fixed 4.00 GHz clock, dominates Geekbench, showing superior performance in everyday desktop tasks and general productivity.

The choice between them should be based on the target workload. For anyone primarily running Cinebench-style render workloads, the i5-8259U is the better performer, winning all six Cinebench head-to-head tests. For a desktop system focused on general responsiveness and Geekbench-measured tasks, the i3-8350K is the stronger option, winning both Geekbench tests by large margins. The i3-8350K also offers a significant advantage in ECC memory support and an unlocked multiplier for overclocking, while the i5-8259U’s much lower TDP of 28 W versus 91 W makes it suitable for thinner, more power-efficient mobile designs. The two CPUs are evenly matched in overall average score, but they achieve that parity through very different strengths.