Well I benchmarked a bunch of computers on the floor of the vendor exhibit and they are faster than mine. But I was soured by the fact that SW2004 running on mine is still faster than SW2006 running on one of them when working with parts. Not to be disuaded from a planned rollout of 2006 I did some more testing. SW2006 did seem to rebuild large assemblies about twice as fast as 2004 so this was good news. But then I tried the next step in pre-rollout testing on SP3 and created a drawing. Oops, SW2006 would cut a section through the same large assembly, but if section scope was used the section failed. On the other hand, when I just converted the 2004 drawing it seemed to work.
Conclusion: Parts slower, assemblies faster and drawings quirky.