PCI latency has no impact on rendering, but your card/motherboard may fallback to PCIE3 instead of using PCIE4, in which case filling the cards entire VRAM from RAM could take an extra half-second (slowing the loading of new textures an infinitesimal amount).

Modern engines also do a lot of streaming data to VRAM, rather than loading everything up front. So it’s not necessarily a single delay and could very well impact framerates etc.

Is there anything out now, or even on horizon, that's materially impacted at running at PCIe 3.0 rather than PCIe 4.0 rates? I can't think of much.