Digital distribution versions are already patched; for other versions use the patches below.
Set Launch Options...
Start-up parameters for the ArmA series are quite complicated due to the engine. An extensive accounting of the available parameters can be found here.
-exThreads=[number] (The number varies. 1 if you have a two cores, 7 if you have a four or more.
Feel free to experiment with this setting to see if anything grants you higher performance.)