Rx1/162
I had (have... but should be picked up and sold this Sat) an 03 RX1 which I put a 162" track on it. I also did an M7 skid... kinda wish I had put in an Apex skid, as the M7 kinda moved back the pivot point on the sled and made it 'turn longer', if that makes sense. Greatly improved the approach angle, and the M7 skid floated like a dream in the bumps, but at times I could tell a difference... reminded me of a friends' sled which had a drop and roll and the skid moved back.
Anyhoo, I did gear it down some, but I did that even w/ the 151" in it. Engine's certainly stout enough to pull the 162" in deep snow... biggest issue w/ it is the weight. If you can pull some weight off (I'd dropped almost 100 pounds) or throw boost on it, really wakes these things up.
I'd go w/ the 04 unless the 03's significantly cheaper... few things better, including updated float bowls, etc. Otherwise, they're great sleds!
BTW, only reason I'm selling mine is to get boosted... am buying Cousin Vinny's 05 Vector w/ a turbo... geometry-wise, is the same frame as the RX1, so arguably I'm not making a chassis-change. It's got a 162" on it as well.
So, welcome to the 4stroke world, and post some pics of your sled once you get it!
Nomad