biggest difference will be the experience of the rider. I have a friend that will run the woods with an 03 RX1 and do well. 3-4 years back he bought a x fire and is the hero now. It's really all about the nads people. Unless you jump from a 121 trail sled to at least a 136 paddle it's not that noticeable off trail. The footprint and pliability of the rubber track is most important to me.
I had a friend that extended a 121 doo to a 136 1.5 paddle and he still sucked riding, always had to dig the boy out.
If your changing tracks regardless than why not bit the bullet and go for the longer track with a larger bit, ext kit ain't all that much cash. A 136 is good for trail also. I threw the 141 cat power claw track on my sled and that track is plain crazy, best money I ever spent. I'm not suggesting that for your application but now what a bit that thing has, it just digs and pulls