For 4.2 ghz, you might to go with watercooling. The highest I've gotten was 4.0ghz, 10 hrs. + on prime (haven't tried OCCT or Linx yet). All of the 9550's I've seen also run at 4.0 or below, but I don't want to speak for all the Q9550 owners out there

. Some of the better aircoolers out there though would be TRUE, Megahalem, IFX-14 if you can fit it, Zalman CNPS10X Extreme, Noctua UH-12P, Tuniq Tower 120X, Hyper 212, V8/10, Xigmatek, etc. There are a ton, but you might be better off with the Corsair H50 (pretend it's air).