The Freezer 7 is perfect for a mild overclock, but then you could get DDR2-800 and save some money. I'm assuming you want more than that, so get a heavy-duty cooler like the Thermalright Ultra-120 Extreme/Scythe SFF21F combo or a Tuniq Tower.
I have WD5000AAKS disks and also WD7500AAKS. The WD7500AAKS is noticeably faster. Also look at the new WD6400AAKS.