With the new machines, I would say a 3320 would be close in most performance categories to the 3720. I have had two 3720's and one 4310. The 4310 torque output was similar to the now 3120. The 3320 has about 8 lb. feet more torque at the same rated speed. My experience with the 3720 was positive. One can definitely tell the extra power is there, but I can say without doubt that it almost has too much power in some cases. It would not pull a box blade any better than the old 4310 did, it could not plow snow much better, although it did maintain speed better on uphills. It did not do loader work better. My only PTO work was mowing, which it did VERY well, but I cannot say it did any better than my 4310 did. Neither machine struggled much with finish mowing. I cannot attest to rotary cutting or heavy field mowing. My only complaint about my 4310 was that it really struggled on my steep hills at my house, especially in high range or during transport work--which I do to excess. The 3720 was clearly better in the higher ranges, but much of my work was not at this level. I feel the 3320 would be notably better than my 4310 in this case. IN my opinion I would seriously think about going with a 3320 v. a 3720 if you bought new, as I would really have a hard time justifying the premium price difference. That said, the 3720 was a powerful machine and did really well. I just wonder if its worth the extra money. I also would say personally I would rather have a new 3320 than a used 3720, unless its a real peach.
John M