also be careful about the actual measurements of the fan. I bought an Orb-like fan/hs from Thermaltake, and the capacitors on my motherboard interfered with the proper placement of the heatsink/fan combo. (ie, couldn't seat right)
make sure it's really a 40mm fan, not a 50mm fan.
also, a fan with ball bearings (IMO) lasts longer than one with sleeve bearings.
DEFINATELY use a chipset hs/fan combo, imho.
~Branson