AMD Radeon RX 6500 XT review: PCIe 3.0 vs PCIe 4.0

The RX 6500 XT is uniquely designed in many ways, not least of which by its PCIe specifications. The 6500 XT uses only four PCIe 4.0 lanes, compared to the majority of graphics cards from both AMD and Nvidia that use 16 lanes instead. That's a worry when many users, especially those considering a budget GPU, aren't likely to have a PCIe 4.0 motherboard and CPU. If you use the RX 6500 XT without these elements in place, you'll be limited to PCIe 3.0 speeds, which halves the amount of bandwidth available - something which could severely hamper frame-rates.

PCIe 4.0 is supported on AMD's 500-series platforms (B550, X570), while on the Intel side PCIe 4.0 became standard with 500-series boards (eg Z590) but is also found on a few Z490 models as well. As a further complication, you'll also need a CPU that supports PCIe 4.0 - for example, our 2020 graphics card test bed uses a 10900K processor so it's not able to access the RX 6500 XT's full speeds.

Therefore, we decided to swap our 10900K for a PCIe 4.0 compatible 11900K to see how much of a difference in graphics performance you could expect to see depending on whether you were lucky enough to have a PCIe 4.0 system or not. We pegged the new CPU at the same 5GHz all-core clock speed, set the RAM to its usual XMP frequency (DDR4-3600 CL16), and ran a subset of our GPU tests twice - first with the PCIe bus at its default 4.0 speed to establish a base line, then at 3.0 speeds to see how much performance we'd lose.

First up is Shadow of the Tomb Raider. We can see a 13 percent drop in performance with PCIe limited to version 3.0, which grows to a 25 percent drop in performance at 4K (not that you're likely to mind given that even at PCIe 4.0 you're looking at an average of 17fps at these settings).

In Dirt Rally 2.0, we see just 70 percent performance at 4K with PCIe set to 3.0. It's a less severe drop of around one to four percent at 1080p or 1440p, where we see more or less expected run-to-run variance between the two configurations. That's good, as it means we're not really being held back in this title.

Far Cry 5 is an outlier - we don't see any difference between PCIe 3.0 and PCIe 4.0, with both configurations taking turns leading.

Metro Exodus comes next, and shows a stark divide between the lower resolutions - 1080p/1440p - and 4K. At 4K, 23 percent of the frame-rate is lost, while at 1080p and 1440p it's only around four percent. Given that this card isn't intended for 4K gaming, this is probably OK, but still not ideal.

Hitman 2 shows a performance drop of around five percent, at least in the Miami benchmark. That's measurable, but not likely to be super noticeable depending on how sensitive you are to frame-time spikes.

Based on our testing, running the RX 6500 XT on a PCIe 3.0 board can sap a decent amount of its performance, even at 1080p, but it does depend on the game. Therefore it makes sense to avoid this card if you're on a platform limited to PCIe 3.0, a list that includes most 400-series Intel (eg Z490) and 400-series AMD (eg X570, B450) motherboards and earlier. Remember also that even with a compatible motherboard, you'll also need a compatible CPU - so while the 10900K and 11900K both work on Z590 motherboards, only the 11900K and other 11th-gen CPUs actually allow PCIe 4.0 to be activated. On the AMD side of things, Ryzen 3000 CPUs and later (eg Ryzen 5000) CPUs support PCIe 4.0, but note that Ryzen 3000 and Ryzen 5000 APUs* don't offer PCIe 4.0 support.

*APUs are a processor plus graphics on a single chip, denoted with a model name that ends with a 'G', like the recent 5600G and 5700G.

AMD Radeon RX 6500 XT analysis

• Introduction and hardware analysis
• Doom Eternal, Control, Borderlands 3, Shadow of the Tomb Raider - Game Benchmarks Part 1
• Death Stranding, Far Cry 5, Hitman 2, Assassin's Creed Odyssey - Game Benchmarks Part 2
• Metro Exodus, Dirt Rally 2, Assassin's Creed Unity - Game Benchmarks Part 3
• Control, Metro Exodus, Battlefield 5 - RT game benchmarks
• PCIe 3.0 vs PCIe 4.0 - How does bandwidth affect frame-rate? [This Page]
• AMD Radeon RX 6500 XT - the Digital Foundry verdict