So you want to take your Quad to 4GHz, your using AIR cooling and you want to buy a cheap case? Am I the only person who sees no logic in this??
You really expect to be able to maintain respectable temps on that Q with a $25 case with poor/no airflow and you don't plan on modding said cheap case yet you still want to OC your quad (aka space heater)? I think your in for a shock.
Don't put a system together like the Intel one listed above and then turn into a tightass when it comes to a case...it makes absolutely no sense and to be honest is a little retarded.
The cases above (Centurion & 690) are both solid cases if you decide to get one...just don't go cheap and regret it.