I have a fair amount of riding time on both 2.6" and the 3". Both on turbo and non turbo sleds. It crappy snow and in bottomless fluffy snow.
My experience with the 3":
For the first 150-200 miles this track wants to dig to the center of the earth. It puts the nose of the sled up and digs down deep. It seems after 150 miles or so the track soften ups a bit and then eases up and floats a little better.
My experience with the 2.6":
Right from the first trip this track seemed to float a little better compared to the 3" that wanted to dig down.
We have had 3 ridiculously deep days so far and I cannot say that I have seen any overall advantage to the 3" track. We had one set up snow day where I did feel the 3" push me around a bit (more noticeable on the 163 vs 155). Once i recognized how it handled it I forgot all about it. I also cannot say that there is any significant disadvantages to the 3".
My personal preference is the 155 2.6. Why? Because I feel the sled reacts quicker with the belt drive and shorter track. I have yet to see the 3" go or do anything I wasnt able to do on the 2.6, and I dont think I will.
The truth is you are going to be happy either way, some people like chocolate, some people like vanilla with hot fudge. Both are great