AMD recently released the entry-level graphics card RX 6400, and the previous RX 6500 XT, only support PCIe 4.0 x4 system interface, unidirectional bandwidth 8GB/s, equivalent to PCIe 3.0 x8.
TechPowerUp did an interesting test, in PCIe 4.0 x4, PCIe 3.0 x4 mode to examine the performance of RX 6400 25 games, 3 resolutions, to see how much worse.
Look directly at the results summary: in PCIe 3.0 mode, the RX 6400 1080p/2K resolution performance has lost 14%, and at 4K resolution, it has plummeted by 23%.
Of course, for this level of card, 2K/4K resolution is meaningless, but it can also illustrate a trend.
Different games also perform very differently, with PCIe 3.0 modes in Assassin's Creed: Temple of Valor and God of War losing up to 35% of their performance, while The Witcher 3 and the like are almost unchanged, the latter being mainly old games.
In addition, games that require large capacity video memory, RX 6400 4GB is easy to not enough, then you have to borrow PCIe channels and system memory transfer resources, PCIe 3.0 will become a bottleneck.
TPU suggests that if you are still using PCIe 3.0 systems, such as Intel 10th generation Core or earlier, AMD first generation Ryzen, do not consider RX 6400, not as good as the previous RX 570 4GB, the price is not expensive, and support the full PCIe 3.0 x16, game performance can be better, sometimes can be as much as 17% higher than the RX 6400.
In addition, the RX 570 and even the RX 400 series still support FSR, which can further improve performance and image quality.