Having never used a VRPC machine I am probably talking rubbish, but I suspect that even on a 3GHz PC, VRPC will feel slower than an Iyonix. My 2GHz PC running Win 2K at work certainly is less snappy in response to the user than the Iyonix and RO5. So assuming that Windows needs a factor of 10 advantage in processor speed to achieve the same responsiveness as RO, one would expect RO running under Windows to be even less responsive than the native Windows on the same hardware.
Obviously benchmarks will run faster on the more powerful processor, but the subjective "feel" of the user interface is another matter. And of course the advantage I didn't mention above, RO's relative freedom from viruses, is lost when running VRPC (although you will not be vulnerable to PC email viruses if you use a RO rather than a Windows email client).