When using such a powerful GPU, might as well jump to the DDR 5 platform. You will get a lot of benefits like being able to use faster storage. It won't impact gaming outside of loading times, but overall snappiness of the system will be noticeable
I don't think there's a difference between PCIe 5 and 4 since current hardware can't use those speeds (neither gaming nor storage will have a noticable difference), but 3 to 4 will have an impact
Also I'm not sure if your mobo supports ReBAR, but that's another improvement for certain titles
I say go for the GPU that will benefit your use case the most.
AMD has more VRAM. There are games coming out that actually use more than 12GB at 4K. But in ray tracing it's just slower, upscaling looks worse, FSR 3 is not fully fixed yet.
That said, Nvidia is cringe in Linux so I won't be purchasing an Nvidia card next, just too many bugs in Wayland