Turning on HyperV to go KVM->HyperV->Windows effectively 'laundered' my VM signature enough to satisfy the anticheats, though the overall perf hit was ~10-15%.
I suspect only a modest hit to average framerate, but I can only imagine it hurt the actual max frametimes which make it "feel choppy" even if the framerate is still higher then your monitor's refresh rate.
I ultimately tore down that setup and just swapped to dual-boot. The steps needed to set up high-performance VFIO (i.e. clearing enough contiguous RAM for 1GB Hugepages) meant most of the benefits of VFIO never really materialized for me.