The only real benefit would be the ability to run 2 faster xeon dual cores but that means more sticks of memory(I think) and I think that people are really pushing it by thinking they'd need more than 4 cores. Hell I still havn't felt the need to upgrade from 1.
Someone told me once that despite having the same instruction set, xeons have lower FPU abilities on similar speeds to their desktop counterparts. He insisted that this applied to all server CPUs, not only Intel's ones. Has this any truth, or should I just forget about it as I have done so far.