why not go for xp/si 120 instead?

well i still believe xp/si 120 is a good choice since the compatibility and the size + performance with avg fans. although it cant perform well as a passive, but comparing the size with the ninja its clearly seen who's the winner already. however, si 120 dont have compatibility issues, fits in most casing too..

but going for high speed fan is another story, there are better options out there. going for passive is another option too, but for overclocking? if you really wanted a silent but powerful setup, get watercooling instead. B)