Hold up there buddy. It depends where you're going and what time of year. If you go somewhere during times with deep loose snow or try to do steep climbs, yes you are going to get stuck a lot. If you don't get too crazy or if you go later in the season when the temps are warmer and the snow is more set up and hardpacked your XF7 will be better than an M IMO.
We've run with XF's and M's side in the same group and they did just fine. They got stuck, but the people who were riding them probably would have gotten stuck anyway no matter what they were riding.
You have to take some of what people on here say with a grain of salt. A lot of people on here talk as if anything but a 162" is junk which just isn't true. 7 days out of 10 the features of a mountain specific sled are a mere convienece. You only really need a mountain sled when the going gets steep or its a foot or more to any kind of packed base. Even then a good rider can ride circles around a novice. Just because a novice rider has an awsome machine, doesn't mean they can utilize its abilities and an expert can make your jaw drop with amazment no matter what they ride.
If you want to get a mountain sled, great, I'm going to, but you don't NEED to. I just figured out the numbers, ask yourself this question: Are you going to ride out there more than five days per year for the next four years (my estimation on the reasonable minimum service life of a sled)? That is the break even point to buy a currant, new, top of the line mountain machine. If yes, you would be wise to buy a mountain machine, save yourself some money, and possibly enhance your fun. If not, rent or use what you have. It costs roughly $170-190 per day to rent a big bore mountain machine not counting that stupid insurance they try to sell you (its a rip off BTW).
If you get lots of trail riding days but want to go to the mountains once or twice a season, the XF is the perfect machine for you- that's what it was designed for. If you're like me and ride out west more than you ride trails closer to home (or the UP) then a mountain sled is a wise investment.