Jstn7477-fps issues and stuff-
that doesn't seem right. I have almost a straight downgrade from that (i5 750 @ 4.0 and HD6950) and I get considerably better fps using chris's max quality config. Are you sure it's not throttling you or anything (thermal limits)?
90% cpu usage could very well be maxing out in this case, because the code isn't perfectly optimized and may have to stall or not make full use of the processor all of the time. But that said, a 3770k at 4.3 shouldn't be that strained to do 80fps. Try using something like CPU-Z while you're playing to make sure you're actually getting 4.3 and it's not limiting you.
Sorry, I guess this is kinda off topic. I may be able to help, feel free to add me if you want.