xp-90, xp-90c, and xp-120 seem to have the best numbers..
xp-120 - original design, very big, pretty light, 1-3C better than xp-90, lots of compatibility issues with motherboards and cases.
xp-90 - new & improved version of xp-120, very light, compatible with most motherboards
xp-90c - the most efficient for cooling, but almost twice the weight of the xp-90 and $15-20 more for only a few degrees.
xp-90c would be the best choice for those who want to pay the extra for a very small difference, xp-90 however is best for most

if you want were to get an xp-120 and one of those ultra extreme delta 120mm fans with 220+cfm, i imagine it would outperform the others by a pretty good bit
