Having owned both, I can tell you the 2520 is twice the loader tractor as the 4100. The extra length and weight helps a great deal with the total lift and the confidence you have when carrying a load. The hydraulics are much faster. Also, get R4 tires up front if you are serious about loader work. The Turfs do not hold the weight very well, compared to the R4s. Another nice improvement of the 2520 or 2720 over the 4100 is the 2xxx tractors are direct injection engines, and the 4100 was indirect. D.I. seems snappier, and is also a bit louder unfortunately (no matter what Deere says).