Well after running with a really solid 60fps for quite awhile, I got to the Marriage counseling mission and was up on the hills with a really big view of the city and lots of grass, etc. My framerate tanked and was sitting around 45-55
I turned off FXAA though I think I want to turn it back on even as ugly as it is.. better than no AA at 1080p. I turned down grass from very high to high. It made a small difference. I think I'll start tweaking down the advanced menu. Long shadows and bringing down the sliders.
I don't want to sacrifice too much visuals but I would always prefer a 60+ framerate than a little extra eye candy.
i5 2500k @ 4.2
EVA 970 FTW
8gigs RAM
win 8.1