I'm now wondering if there will be a difference in performance between the 2.66GHz W3520 for $284 in the 4-core model and the 2.66GHz X5550 for $958 in the 8-core model? I mean, for 3x the price, I would certainly think so. But the single core benchmarks that I have seen has not showed that.
4-core - 8-core
QPI: 4.6 GT/s - 6.4 GT/s
TDP: 130 W - 95 W
memory: 1066 - 1333