An idea that might help. Try turning your camera above your character and away from the main part of battle. I play on a very fast pc, and while I don't experience this issue half as bad as some of the posts I've read here, I do see it happen still. I've used this camera method on many online games, so much that its just natural for me to do it when I play in large scale battles. Basically your pc (or ps3), can only draw so many things on the screen at once (and you have to realize, the ps3 is a very slow system). By turning the camera above and away from the fight, the game will "Cull" anything not on camera, freeing up resources to draw what is in your field of view.

I don't propose this to be a fix in any way, but for now, it might help.