I saw a post a while back that was talking about track length. The person who started the post was saying that he rode trails most of the time and would occasionally do some boondocking and may go to the mountains once or twice a year. I can't recall if they were talking Yamaha 4 strokes or not.
But that thread got me thinking. You can run a long track mountain sled on trails. It's not ideal and you're not going to be the fastest most nimble sled on the trail, but it works. It will get you from point A to point B. But running a trail track (121-136 with 1.5 in or less lugs) in deep powder would be a total mess bordering on un-doable. I've seen guys do it, but they have to keep it pinned all the time and keep their speed up or they're going to trench in.
I remember seeing a friends kid riding a new Polaris with a trail track a few seasons back. He's a really good rider and was running the hell out of that sled, but he was stuck all of the time. And this was set up spring snow with a fairly new, lightweight sled and this kid may have weighed all of 150 pounds. And he was a good rider. Any time he was trying to climb any kind of incline that wasn't tracked up and beat down really good, he was stuck. I remember seeing him at the base of a small hill with a shallow grade trying to get unstuck. It was heartbreaking to watch. He'd sidehill for a bit and as soon as he tried to turn it uphill, he'd trench in and have to dig out again. This went on for a good half hour. When he finally made it to the top, everyone cheered.
I ride an RX1 mountain. It is heavy as hell and came with a 151 track. I don't know what you know about the RX1 mountain, but the factory 151 track and suspension puts about as much track on the ground as a 144 from most other brands and it came with a 2 inch paddle. Everything went pretty well until I was on a winter moose hunt north of Fairbanks once and there was chest deep bottomless, fluffy powder. Any time I didn't have it pinned, I was trenched in and stuck. That was some of the most exhausting riding I have ever done. Needless to say, I decided to extend to a 162 track with 2.25 inch paddles after that trip and have been really happy with the additional flotation of the longer track. I can still ride it on trails, but I couldn't imagine riding back country with anything less than a 151 on that sled.
Now, the Viper is a different animal, but I agree with Motorbreath and wouldn't want anything less than a 2.25 inch paddle on it if you intend to any amount of back country riding. If it were me, I wouldn't go with anything less than a 153. If you are going to ride deep powder, flotation is a wonderful thing. And it will work on the trails, just not as well as a trail sled.
So that's my two cents. You can use a mountain sled on the trails, but are going to have a really hard time using a trail sled in the powder.