Try www.Trailconditions.com It is ok for trailconditions and some general info. There are lots of Magazine Websites for more info. Do a search for "snowmobiles" and all kinds of sites will come up for you.
The 136" will be nice over stutter bumps because it will straddle the bumps rather than fall in between them. It will be better in deep snow (snowshoe affect). It will be a little tougher in tighter trails. It will push through the turns and the turning radius will not be as good. The 136" will also be a little slower across the lake (top end) due to the track weight. There are pluses and minuses to both. It depends on what kind of riding you will primarily be doing. Hope this helps.