Regarding the choice of tires: the R4's seem to be a popular choice, and when ordering my tractor I specced those out (not out of any particular experience, but just the fact that I liked the "manly" looks of the industrial tread). The JD dealer strongly advised me to consider the R3 turfs instead. His reasons (closely matching those of an independent and highly knowledgeable person) were the following:
* on a small tractor like anything in the 2000 series the turf tire "floats" better under most ground conditions
* the R3's will make larger surface area ground contact due to the tire and tread shape (and lower operational pressure), effectively increasing grip
* when spinning in wet clay both the R3 and R4 will quickly turn into a slick ball of slime, and they suck about equally. R1 ag tires would help in these conditions.
* for winter conditions and heavy snow a turf tire with chains will provide the best grip, bar none (short of running on tracks)
I would usually be suspicious of a dealer pushing me one way or another on a choice like this, but he had no obvious reason to do so; there was one 2320 with R4's arriving at the dealership quickly, and going with R3's just made the tractor a special order and added to the wait time. I got similar feedback from several other sources on this question (including several people on this board).
Now that I have the tractor, I have worked it in my woods and my fields, as well as digging with the FEL and moving dozens of yards of material. I could not find fault with the turfs, and could recommend them to anyone. That is not to say that I am poo-pooing the R4's as the only fair way for comparison would be to run two tractors with the two different treads side by side. But my experience has been that the R3's are giving me superb grip under normal or dry conditions, but they are NOT recommended for digging in a clay pit in the rain

. As an added bonus, they have been forgiving on my lawn when I did some sharp turns with 4WD engaged. As far as the winter performance goes, I will be able to speak to that in six months.