Starcraft II bottleneck?

So I play a lot of StarCraft II (pretty much the only game I play) and I have some fps "issues" for the most part the game runs fine on any settings. It's when I get into big battles (200 vs 200) that I run into some major fps issues. Now being that I am a competitive player I play the game on all low settings at 1440x900 resolution. I just want to be able to hold a solid 60 fps no matter what...