Another tip. :D
Run ArmA2 with High CPU priority. This gives more time for processing with ArmA2. For me it gives about 10% more performance when there are plenty of units on the field. In games such like Domination and Warfare etc I've noticed going from ~27FPS to ~30FPS. To run ArmA 2 with a high CPU priority you can go to task manager and right click arma2.exe and alter the priority that way. Alternatively you can edit your target line on your shortcut.
Add this to the front:
C:\WINDOWS\system32\cmd.exe /C START "ArmA 2" /high
C:\WINDOWS\system32\cmd.exe /C START "ArmA 2" /high "D:\Program files\Bohemia Interactive\ArmA 2\beta\arma2.exe" -world=empty -nosplash -winxp -mod=@ace;@acex;@acex_pla;@acex_sm;@cba;beta
:) Hope that helps some people.