Do you need to have a Small Desktop? I understand you want it to fit well in your dorm room, however, if you think you would be ok with a bigger case you can get bigger hardware with more airflow and performance by allowing for more room.
More then likely that 6750 will fit with it being low profile.
Just a suggestion if you do consider a mid size case that holds a full size ATX MB
I would not be able to do a full size case, I currently have a full tower AMD Phenom I quad core setup and the thing is too clunky to fit anywhere. A micro-atx style case/motherboard may be doable, any suggestions? Ive heard good things about the HD6870 as well. I'm trying to keep my budget below $700 for an entire build.