The 990 Pro is the throughput king: higher rated and measured sequential speeds, stronger sustained-write performance, and better efficiency. The SN850X counters with game-load wins in published head-to-head tests, gaming features, and a usually lower price. Video editors and heavy writers should pick Samsung; gamers and PS5 owners get more value from WD.
— THE VERDICT · JUDGEANY EDITORSTwo flagships, one PCIe 4.0 ceiling
The Samsung 990 Pro and the WD Black SN850X are the two default answers to "what's the fastest PCIe 4.0 SSD?" — Samsung's all-in-house flagship (Pascal controller, 176-layer V-NAND) against WD's gamer flagship (in-house controller, Kioxia 112-layer flash, Game Mode 2.0). Rated speeds: 7,450/6,900 MB/s for the Samsung, 7,300/6,300 MB/s for the 1TB WD (6,600 at 2TB and up). We run no test lab; this piece aggregates manufacturer specs, owner feedback, and published measurements.
Sequential speed: Samsung's territory
On paper the 990 Pro leads, and measurements back it up. Windows Central measured 7,465/6,850 MB/s — essentially the rated figures. In a same-board head-to-head, Custom PC coaxed 7,198/6,754 MB/s from the Samsung while the SN850X never broke 7,000 MB/s read; the 990 Pro also took the high-queue-depth 4K random read test (3,105 vs 2,840 MB/s) and PCMark 10's full-system trace (520 vs 463 MB/s). A separate PCMark 10 run on 2TB models (Storedbits) scored 4,680 vs 3,850 with 22% higher bandwidth and 16% lower latency for Samsung. Moving huge files — 4K exports, big archives — the 990 Pro is measurably quicker.
Game loads: WD claws back ground
In that same Custom PC comparison, the SN850X won the single-queue-depth 4K tests and loaded games faster: Battlefield V at 1,154 vs 1,035 MB/s and Call of Duty: Black Ops at 965 vs 739 MB/s, with lower access times. Tom's Hardware's testing of the SN850X found Game Mode 2.0 made no difference in ATTO but trimmed latency slightly in CrystalDiskMark's 4K tests; it called the drive "one of the more consistent and well-balanced Gen 4 SSDs" and its top PS5 pick. Reviewers split on low-queue-depth reads — Tom's own 990 Pro review called those "the best we've yet tested" — so treat the gap as small either way.
Thermals, efficiency, and sustained writes
Both drives run hot under sustained load. Custom PC watched the bare 990 Pro hit 75°C in a stress test; Tom's measured the SN850X at 78–85°C. Either way, a heatsink is effectively required for full speed, and both makers sell PS5-fitting heatsink versions. Samsung claims up to 50% better performance-per-watt than the 980 Pro, and the efficiency edge shows in testing: Dexerto measured the 990 Pro 4TB peaking near 5.5W against roughly 7W from a rival 4TB drive. For long continuous writes the SN850X has the deeper pSLC cache — roughly 600GB on the 2TB model per Tom's Hardware, versus 226GB on the 2TB 990 Pro (TechPowerUp).
Software, endurance, and one caution
Endurance is a wash — 600 TBW at 1TB, scaling with capacity, with five-year warranties on both. The SN850X claims a longer MTBF (1.75M vs 1.5M hours), though that's a spec-sheet number, not a promise. Samsung Magician remains the more polished toolkit: health checks, cloning, firmware updates. WD's Dashboard — and the exclusive Game Mode 2.0 — runs on Windows only. One blemish for Samsung: early 2023 reports of 990 Pros showing rapid health declines turned out to be a firmware bug, fixed by the 1B2QJXD7 update that February (Tom's Hardware, Neowin). Check the firmware in Magician on any unit you buy.
Price and the verdict
Buy the 990 Pro for the fastest sustained PCIe 4.0 throughput and the better efficiency — and expect to pay the usual Samsung premium. Buy the SN850X for gaming: it loads games as fast or faster in published game-load tests, usually costs less, and Tom's Hardware still rates it the top PS5 drive. Creators moving huge files go Samsung; everyone else gets more for their money with the WD.
