I upgraded earlier this week. Version 5 is faster than version 4 with XP. I have not compared benchmark speeds tho.
I don't doubt the claim that they sped up their code, and good for them.
I'm only saying that (except for a rigged case) virtualization can't run faster than native code on the hardware (unless the native code is really stupid-slow). If Parallels has figured out how to make software that runs so fast that it actually beats the hardware, somebody will be in for a Nobel in Physics -- they'll have invented the equivalent of a perpetual motion machine!
I've generally used VMware products, but a few co-workers have used Parallels and say it historically has lagged behind VMware in speed and features. I suppose this means Parallels is catching up, which is good.