Tracks usa makes them if you want to run the small wheels in the rear. CB Performance made me a set 144 tiped up for 8in rear wheels. The geometry of an M10 is screwed up in stock form as it is, I never found my 136 version I ran to have any problems with track tension with either the small wheels or the offset axle I ran the second year. I found Fast to be not so wonderful to talk to about extensions on their skids or references to larger wheels. They told me that they don't recomend it. They were also trying to sell me a set of 136 rails instead.
When you do this, make sure you do not adjust your track to yamahas sag spec for the track tension. The geometry of an M10 is messed up, it tightens the track as it is compressed so if you adjust the sag to an inch hanging, it is banjo tight when you sit on it and even tighter hitting a bump.
you will love the extra traction, as far as ride, I saw no difference in ride between short and long sled, its only 7.5 inches longer, but the extra track on the ground does hook and float better. If you havent bought a track yet, I would go right to 144, not sure if I would bother with tipping up rails again though. I am not changing mine back but the next one I think will be flat railed.