Depends if you can get a 1ghz overclock. With a non-stock heatsink and probably a tiny voltage increase you would get better performance. A 1ghz overclock generally would be noticable i think, especially on a Core 2 Duo/Quad
also i have the Antec 900 case and as of right now my temps r running at minimal load between 32 and 40 degrees ... i think this machine will overclock very nicely..