The most surprising thing that we noticed while comparing our new findings on the 2.6 kernel with those of our previous report (32 bit, 2.4 kernel) is that the Xeon benefits a lot less from 64 bit and the new 2.6 kernel than the Opteron. While the 64 bit binaries run consistently (much) faster on the Opteron, the Xeon isn't too happy with them and runs them 4 to 10% slower. Hyperthreading isn't - in our case - helping either, with 1 to 10% lower performance
An interesting look at how the two companies server CPUs stack up and perform when comparing 32 and 64 bit processes, as well as dual core CPUs in comparison to dual CPU setups.
It's a bit odd how the Xeon loses performance both when exposed to 64 bit applications, and with hyperthreading enabled. I wonder if Intels desktop CPUs will follow suit.