Running an old dual core 3 ghz, 4gigs of ddr2 ram and a 760gtx 2gb video card. Plays smooth on Ultra at 40-60fps. Using Windows 7 x64.
Wow! I have 2GB GTX660 OC (not hugely behind a 760) 8GB RAM and Q9550@3GHz (quad core). On High I get between around 30fps (dips to 25, peaks to 40) on the surface in the SRV but low level flying is around 20fps depending how much terrain is shown. This is at 1920x1080 with 1.0 supersamping. What Res are you running?
Obviuosly I may turn down some settings in the long run but still experimenting at the moment. Given the low fps sometimes its not too bad smoothness wise.
I was looking to upgrade the PC in the new year but not sure what GPU too go for given the variety of results from various places in the forum. Was looking at a GTX970 but now not sure if need 980 980ti to be safe. (Sorry, not an AMD fan)