Been playing the demo & I have found that it does not support/use crossfire I have played the normal & steam copys of the demo.
I get 30fps with crossfire on & 35 fps with crossfire off.
Does the full game support crossfire ?
I have found a fix to make crossfire work with the full game but it does not work with the demo as the .exe does not have the same name.
Fix is below
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Solution:
1. Firstly set your CAT AI to ADVANCED
2. Rename Arma2OA.exe to Arma2.exe (Other crossfire games may work)
3. Start up Arma 2, you should now see that both GPUs are being used.
DO NOT USE THE -WINXP COMMAND!!! THIS WILL DROP YOUR FPS BY HALF
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I can't play the game any sense with a fps less then 45 as it's not smooth when aiming.
I have looked at the activity of my other GPU's when finshed playing the demo & they show 0%.
Forgot to add link to post where I found the fix
http://forums.bistudio.com/showthread.php?p=1660910#post1660910