I have been working with "smoke" recently in Blender....
trying to create a fire breathing Dragon.....
holy crap smoke is a huge FPS killer, so bad, I don't think I can actually get it to run good on my system and will have to use, images instead of a particle system. 
I put together what I thought was the second best PC two years ago, 30 inch monitor with the whole 9 yards. When I look at a hanger on fire my FPS drops to the teens. My PC right now is the top of the line, I look into a fire in Aces my PC crashes.
I cannot figure out what causes my PC to go nuts when looking at fire in aces, usually its 60fps in every situation except fire/smoke. Most bran new games the graphics don't even flinch, but in aces fire/smoke just cause it to go nuts, such a loss in FPS makes the game unbearable to even play.