I averaged 48 FPS with ultra settings on my 09 core 2 duo 4670. In dungeons it would hover around 80 FPS. When I switched up to the 5670 I am averaging around 55-60 FPS and 90-115 FPS in dungeons. All on ultra. You may have an issue somewhere if your running that low. The only time i dip into the low 30's is when I'm in Dalaran while it is very populated. like outside the Bank.
I am using Titan Panel for my FPS numbers and averages.
Forgive my ignorance, but is that under the mac osx or are you playing it in bootcamp?