Well I was just about to make a thread about this.
i7 920 4.3ghz
GTX 580 3gb x2
12gb DDR3 triple ram
win 7 x64
5760x1200
Running the game DX10, x64, max settings, 12 AF, 8x AA.
MWLL 0.4.9 Average FPS was 40-50fps, 30fps on frostbite. Game completly playable and almost completly smooth.
MWLL 0.5.1 Average FPS is 20, 10fps on SA. Game completly unplayable, juttery and stuttering all the time. SA turns into a slide show. Top of hanger FPS has gone from 90-120fps, to 30, hell it sometimes drops lower.
Needless to say, I am NOT HAPPY.
I've tried disabling AA, and AF, gained 0-2 fps. I have deleted the shader folder, and I even reset my Nvidia 3d settings in case I changed something and forgot. The game just runs like shit

Anyone got any suggestions?
P.S, I will try running warhead, and seeing how well it runs, I will also try running the game on a single screen. But other games like BFBC run flawlessly at 60fps on max settings.