I got Windows Vista 64bit, Geforce 295 GTX and the Steam version of ArmA 2.
ArmA 2 only used one of my cards GPUs (SLI mode wasn't working). I tried the EVGA patch and all the other tweaks but they didn't work either. Afaik the EVGA patch just makes a crysis-like profile for arma2, so I tried to do this manually with nHancer (http://www.nhancer.com/?dat=downloads) and it worked:
First I did a clean 186.16 driver install with Drivers Sweeper. I then opened nHancer and duplicated the crysis profile (right click crysis profile -> dublicate profile).
From the new ArmA2 profile I disabled SLI DX10 Mode (from SLI DX10 tab, not the regular SLI), also disabled Hybrid SLI and Hybrid SLI DX10 modes from SLI tab. (For testing purposes I also enabled the SLI Load Balancing Graph, check box + the ON radio button). From Enhancements tab I disabled Vertical Sync.
Then I added the arma2.exe executable (Steam\steamapps\common\arma 2\arma2.exe) and Steam.exe as a launcher. I didn't know if that's actually considered as a launcher so I added another arma2.exe just in case, without the launcer. To get the SLI load graph working I also checked the "Profile be activated manually" and activated the profile from the menu (Tools -> Activate Profile -> ArmA2).
I ran the game from the .exe (with steam online) and SLI works! FPS in menu increased from 50 to 100 and in-game fps raised a lot as well.
After confirming it works, you can disable the SLI Load balancing graph and set Driver defaults from the menu (Tools -> Activate Profile.)
Hope this helps people struggling with multi-GPU and the EVGA patch.
