[Ray88]

Someone could have sli 1080, ,but be running a 3rd gen i3 or i5, I've seen crazier like Pentium G3258 & sli 970, which would be severely bottlenecked by the cpu

I really doubt that. Even an i7 2600k oc to 4.3+ ghz wouldnt cause a severe bottleneck on a 1080. Modern i5 cpus are fine as long as the game isnt heavily cpu dependant.
The pentium is OK imo as its a dual core with 2 threads and most games do still run on 2 cores. OC that bad boy to 5 ghz under liquid and it'll be fine. I've seen guys get almost near performance as a i5 4690k in games when they oc their g3258.