I ride Marathon Winters (1.75 wide) as my primary winter tires but I keep some aggressive cheap 2.1 studded Innovas around as a bailout set for when I might deal with 4" or more fresh snow.
REI is closing out some 2.35 wide Klondikes that will get me pretty close to a baby fat bike.
My concern is that the 2.1 tire is about as wide as my fenders which are velo orange stainless. The 2.35 will be too wide but that's the next question - how to make stainless fenders wider. For now I'm asking about the tires... Reviews are hard to come by so tell me what you know!
I am going to answer this for myself. I ordered the tire, mounted it on a 31mm rim, took some pictures and measurements, and took it off.
Basically, because of the tread pattern, it has a more narrow contact area that the Innova 2.1.
The 2.35 measurement is the farthest outside sidewall width that I could get when I had 60lbs in it. The sidewall bulge is much wider than the tread, unlike the Innova where the tread is wider than the width of the sidewalls.
Note the tread and layout pattern and how the 2.1 Innova yields a wide contact area than the 2.35: