I owned an 08 XP and a 2011 Pro last year, and have ridden an XM a couple times.
If you like your XP and like Doo, just buy an XM. It does everything the XP does, and more, with less rider effort.
Personally, I never much cared for the XP (wound up with the 08 just cause it was a good deal). That said, it was MORE than fine enough to get out and play around on, but lots of our riding gets fairly technical and it just doesn't shine there.
The Pro rides a lot differently than an XP or an XM. Seating and standing positions are different, suspension feels different, engines feel different, everything. They both do basically all the same stuff, but the feel is not the same. The Pro has notable advantages if you really push steep sidehills as part of your riding. If not, you could argue the rest of the pros and cons all day and not come up with a clear answer.