Without knowing what you are going to be doing with your tractor, and under what conditions, it's hard to answer. But considering that you are talking about a 5105, I assume that you have some heavy duty work in mind, and you're not using it to mow your nice lawn.
I have ag tires on my 4320 and if I didn't, I might as well forget about using it in the winter (I live in Oregon, where it does rain occasionally). Yes, I do tear up the ground when it is wet, but I would rather do that than get stuck.
I say go with Ag tires for that beast.