What brand was your HD6870, bullet?
Are you saying you could run it with max settings and still obtain 60 fps?
On one of my pc builds I have the AMD Q975 3.6 GHz quad core with 16 gigs of system ram, and use an XFX HD6870 1024 MB VC... OS being Windows7 ultimate sp 1 64 bit...
Using the 2048 texture setting in the login screen video settings and in-game graphic settings every thing turned on/checked, I can only obtain a constant 60 fps at 1920x1200 screen res, when the environmental slider is turned all the way down or just using the first notch only...
TC