I noticed when firing on full-auto that you get an unnecessary framerate drop. Since shooting is a pretty basic thing in ArmA, I think it should be optimized.
Here are a few framerate comparasions:

Base framerate: 54
Framerate laying prone (with particle effects) on low: 43 (That's 11 FPS!)
Framerate standing on low: 44
Framerate laying prone on high: 39
Framerate standing on high: 36

These framerates were taken to be shown here when they got the slowest; it happens usually after 30 rounds, the size of an average magazine.
Other thing I noticed is that this FPS loss is a lot more evident when playing a multiplayer game, when you're actually shooting someone and missing due to fps's lost during this event.
Workarounds:
Possibly add a lower setting for particles (Some people, like me, care only for framerate)(I realize that the particles aren't the only thing that kill fps.)

*Why I think this should be addressed? Firing a weapon is very common in a game like this; having such framerate drop isn't very appealing.*