We had lots of big Brent wagons before switching to semis.

My experience says the big super-single wagons will get stuck much quicker than a grain cart, if it's a little soft. Wagon starts going down, tractor spins, wagon goes down further....done. We used pretty good size tractors on the wagons also.

Also, in the great state of IL, the St Police often weigh big wagons & administer "healthy" fines. You're allowed 36,000 lbs GROSS on a wagon, no matter what. That's it. So, that means about 570 legal bushels of corn.