I'm actually in the process of trading in my P1 for a P6 right now. As to which is the better buy, I'd probably have to say they're about par with one another. Both used trade ins at roughly the same price, same round and capacity, both show poor performance with HPs, etc. Really, it just comes down to your own personal preferance, which is why I'm moving to the Sig.
A word of warning though, if you decide on the P6, expect outrageous magazine prices as the amount available is quite low.