> which doesn't approach the single-core speed of the Power systems.
It does. Easily.
New Xeons beat all the PPCs except for the top-of-the line POWER-7 CPUs. And then top-of-the line PPCs beat Xeons only because of their humongous die size and clock speeds (with corresponding TDP).
In reality there's no magic sauce that makes PPC to be inherently better than x86. They both use hardware decoders to split instructions into pipeline-able sub-instructions. Sure, decoders for RISCs are easier to implement but the difference in the number of transistors is trivial for desktop/server CPUs.
I'd several run-ins with IBM mainframe guys about a year ago. They told my client how great and fast their mainframes were, that $100000 per system couldn't be wrong, could it? So my client went and leased a 'small' unit - telling how great it would be.
IO turned out to be slow as hell compared to our simple Xeon-based server with a RAID of Intel SSDs. CPU performance indeed was higher, but not by much - and we got one of the fastest CPUs available.