out of all the replys in this thread I didn't see anyone ask the obvious questions:
1) The stock heatsink comes with thermal strips applied, did you remove these or just add more TIM?
2) Is the heatsink properly seated? (we all know how much of a pain those push pins can be don't we?)
On the case issue, it is an ATX form factor case, almost any aftermarket cooler is going to fit.
Guys, slow down and address the causes before running on with ideas.