Ken,
I guess a lot depends on the size of your equipment, how fast you have to get it done, the terrain etc. I have a neighbor who does his haying with a 30hp +/- Ford CUT. He has a small baler and only does a few hundred bales. He doesn't use kicker wagons, just bales it on the ground and picks it up. If you have several thousand bales knocked down you (at least I) do not want to be picking them up in the field. If your bales average 40 pounds and the wagon weighs in the neighborhood of 2000 lbs (guesstimate), that 10,000 pounds for just a loaded wagon. Add in the baler and your starting to get up there. I have hauled loaded wagons with my 3830 to the barn about a mile down the road. As you probably know those 4 wheel kicker wagons are about the unstable meandering things you want to pull over the road. I go slowly, but I suspect it would not take much to throw a 4600# tractor (w/loader) out of control, especially going down a steep hill. My Kubota manual (page 11) says the maximum load for a 3830 is 5500 pounds including the trailer. The 5030 is rated at a total of 6600 pounds. So I guess I was pushing it. (I have heard the three times the tractor weight theory, so I guess I was ok with that!) As you have pointed out it can be done and I agree with you on your point.