As said I am running two XM 872s that my boys ride. They are so smooth and crisp that they deceive you a little with the power they make. Here are a couple of examples. My son broke his collar bone clean thru about 8 weeks ago and hasn't ridden his sled much so it is still in break in mode. They make a little less power in break in. I had my other boy ride his sled last weekend and it caught him on a steep climb in dense wet snow and wheelied over on him. Just a quick stab of full throttle in good traction and it went right over with a 230lb rider. I ride a 900 Pro Lite which before this weekend I swore had more beans than the 872s. Its loud and rorty, hits really hard in the middle and has dragged my big butt up some pretty treacherous steep climbs. We drag raced the two of them on a small lake. The 872 was a sled to a sled and a half ahead at 250-300 feet. The 872 has a belt drive and stock track, the 900 has a 3" X3 track and belt drive. Clutching on the 872 is really close(Roosterbuilt) and the ProLite needs a little more clutch tuning but it's getting max rpm, just not as hard in the middle as it should be. We swapped out 4 different riders and the 872 won every single time even when the ProLite was ridden by a guy who weighs 50lbs less. Never would have believed it if I hadn't been there myself.