I don't think the P6 is an upgrade over the P5, not much of one, if any at all. It's a shame you weren't looking a couple of months back, when dealers were closing out the P7 line for around $1800 brand new. That was a nice step up over the P5 at a great price, but as far as I can tell, they are all sold now.
That leaves you with a P8 ($3000-$4000) or a P9 at $5000.