I have a MX5100 2wd. I have gotten the tractor stuck, but backed out with the bucket. I have plowed snow with it, dug holes, and have not had any trouble with it. I do keep a ballast box on the back when I am doing a lot of bucket work, but that is all.
I think that if I had 4wd, I would get in a lot more trouble with it than it is worth. Most people use 4wd to go forward till you get really stuck. On a tractor it is good for doing bucket work, or pushing. With some ballast in back, diff lock, I can do almost anything I want. It is a great tractor, remember I can always do smaller work with a big tractor, but I cannot do bigger work with a small tractor, so if the price is right and you decide you are ok with 2wd, then get the tractor, you wont be disapointed if it is in decent shape.