Corn seed pro boxes can get upwards of 3k, depending on variety
A bag of soy beans will fill a probox. We've done it for replanting.
Beans tend to be a bit heavier than corn, by volume, depending on moisture content, variety, etc.
I'm not a farmer, but I have dicked with more speed bags full of beans than I care to think about. I know they'll get the forks bouncing on a 7k forklift going over the barn threshold.
I think its 23 or 26 bags to fill a 48' hopper bottom....not according to weight, but volume....prob over legal weight, always are.