crash - I ride Poo, but before I bought my 800 RMK 144, I was looking REALLY hard at the SkiDoo Hillclimb. That thing rips. Or the Summit X 146. The Hillclimb is 154. They are lighter than both the M and the Assault/RMK's. I think they've fixed the problems they had with their motors too (cranks and belts, and something else).
But I think these guys are right. You really need to think about what you want. The Assault is really set up to do big time boondocking, jumping, especially in heavy snow. The trenching in soft new powder will be troublesome if that is where you are riding. Just has to do with the track lug. The shocks are really stiff. The M is a mountain sled. If you want so stick with Polaris, look at the Dragon RMK's. They have the bells and whistles that Assault does, but with a mountain track.
I don't know much about the M's, but I've always thought they seem to be pretty darn good mountain sleds. I just never cared for what appears to be a low seat.
Good luck. Be sure to post what you end up doing.