151 is the answer
I had the same question a few years ago. I came to the realization that going to a 151 was the way to go. Best decision I made. MPI was a little slow at getting me the extension kit, but it worked great. Climbed better, could still boondock great, and went throught the pow like crazy. 151 tracks with the 2.5" pitch have been available at Haydays, Craigslist, Snowest, and here. Used extension kits can be found too.
Here's the kicker: The 151 track I bought weighed the same as the heavy Yokohama 141 without porting it.
my 2 cents based on my experience.
Eric