Compute, especially asynchronous compute is heavy on the PCI-E bandwidth... And some games will leverage that more than others.
Either way, PCI-E 8x is probably not worth our time as gamers in 2020... Especially as GPU's are set to jump in DRAM.
PCI-E 4.0 8x/PCI-E 16x is probably the minimum going forward.
--::{PC Gaming Master Race}::--