My experience in riding on plowed/salted/sanded roads in the winter is that you don't want the widest possible tires - narrower tires will more effectively cut through the mashed potato slush and contact the pavement underneath.
Also, as said above, the salt will destroy your $2000 fat bike as fast as it destroys a $50 dumpster bike - the only difference is that it doesn't hurt as much to throw the $50 bike back into the garbage bin where you found it.
I bought a nice fatbike for winter riding, but I am planning on only taking that bike to the snowshoe trails. I built myself a winter 'beater' bike with 1.75" wide studded tires because I don't want to ride my fatbike on the road in the winter.