Umm, yeah, the FOP 38 is good enough to overclock. It's basically considered one of the best, if not the best HSF on the market right now. The only problem with it is the fan, which is annoying and loud. It sounds like a hairdryer. The FOP 32 is the same heatsink with a quieter fan. There is a recent HSF roundup on anandtech that should help you make a decision.
A power supply fan is generally not considered a case fan. Most cases have cutouts in front/and or back for additional fans to be installed. If the cutouts aren't there, you can mod your case to put them there.