It will only be a problem if you fill up VRAM and the app has to go to system RAM, similar to filling up system RAM and needing to go to the page file. 8GB is more than plenty for that card, so you likely won't fill it.I want to buy a sapphire pulse 5500 xt 8GB that have PCIe 4, but I don't have a PCIe 4 motherboard.
Will PCIe 3 affect a lot the performance?