I got to ride one up at the expo in west yellowstone. We were on really hard pack so keep that in mind.
The pro was a nicer ride on the trail, and had smooth engagement compared to the m8. Didn't like the handle bar set up and the pull cord was way too long for a shorter person like me. This being an issue since in order to start them you have to pull the cord all the way out- no half pulls.
The m8 has a lot more power, the seat is way comfier then the pro, the adjustable handle bars are very handy, the m8 does have a bit of vibration but you get use to that very quickly. The stock skis stuck.
I know the cat handles really well in the powder, can't comment on the poo since I really don't know.
I would say it depends on what you are looking for? Something smooth and easy to ride on the trails go with the poo (if you are brave enough to trust polaris' engines after all the trouble they have been having.) If you are looking for something very powerful stock yet reliable and just plain fun to ride go with the cat.