Get the 4940C, it's a wonderful tractor. Being 4 wheel drive it delivers exceptional power and well the cab, what can I say, I would never have another tractor without the cab, it makes all the difference. When you consider the lifetime of the tractor the difference of the cost for the cab will actually turn out to be pennies.
Good luck with which ever Montana you buy, I know you'll be happy with it as I am with mine.
Glenn.