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!