"I am talking about loading a single figure, no props, posing and rendering from scratch."

I'm thinking there is something wrong with your P7 copy; I've been doing some testing between P6 and P7 on both my desktop (Athlon 64 x2 4600) and laptop (Turion MT-40) and I've been finding P7 is always faster. Just to rule out the obvious, are you sure it's not stopped because there is a missing path or geometry file? Sometimes the prompt is hidden, but it seems to freeze up the whole program. Also, what kind of video card is it (what Geforce series?) Do you have all updated drivers?