The XT for all intents and purposes is the best block available, less restrictive than the HK, requires less precision when mounting than the HK, and more readily available. For a CPU only loop i dont really recommend going with an XT and a double swiftech, your temperatures would be better off going for a better rad such as a BIX, SR1, RX, or one of the new EK radiators and a GTZ, because how much heat you can dissipate matters more than the waterblock, only with a nice radiator would i recommend spending the extra on an XT.
so how about a gtz block and a ek xt 360 rad what pump and res then.?