It's not just the processor, though, it's emulating all the support chips as well. VPC is emulating the CPU, the RAM controller, the PCI bridge, the video chips, the sound, ... even with a modern VPC doing dynamic recompilation that's a big load to do.

Admittedly the PC is not a complex or highly timing dependent system like, say, the C64 or the SNES, but it's still a heavy haul for a G3/250 with a relatively slow system bus.