PCIe 4 vs PCIe 3: Is it time to upgrade your motherboard?

It should be backward compatible, but you will see less performance than if you had it in a PCIe slot since it runs at PCIe x8 instead

After a quick Google search, I found this article which explains that: a PCIe x16 slot can theoretically hit approximately 32 gigabytes

pciex4 slot Scalable parallel computing GPU dense servers that are built for high performance 2 GPU 4 GPU 8 GPU PCIe PCIe x 16 Slots 7 · 6 · 5 · 4 · 3 · 2 · 1

pcie 4 ssd in pcie 3 slot GPU's with waterblocks are even narrower, generally a bit more than 1 PCIe slot wide You have three options for a 4 GPU rig, blower style GPU's