given the choice i'd go with the blademasters, but more due to previous experience with them - i know they shift alot of air & do so at reasonable noise levels. For a radiator in a water cooling loop high static pressure is essential due to the density of the fins, air coolers generally aren't as tightly packed. as for why coolermaster dropped the fan to a crappier model... cheaper i guess?
Dude I've been trying to find which fan the evo comes with all week so that I could match my rear case fan to it and share the PWM. Thanks for the info although I think I will actually just buy 2 blademasters rather than an extra XtraFlo.