Fact is, my i5 2500k could only manage about ~60fps in intensive scenes/looking at a lot of the map in Shanghai. My 3770k does more like 75-80. The IPC and 0.2ghz bump over my 2500k would only account for a 10-15% increase but i'm getting more like a 25-30% increase so the hyperthreading is definitely doing something right. Even with the 3770k my GPU's still aren't being used at 100% on a full 64 player multiplayer map.
I'm not saying hyperthreading isn't helping, it surely is doing a lot of good.
I am saying an I5 Haswell with a mild OC will not be bottlenecked by any single GPU.