Maybe with 1000lbs on the 3pth? on very level ground, very carefully. Seems like you could move them with a 3pt spear ok, but on the loader in a field or barnyard, I think you are too close to the max for regular use.
I used to just slide 4x5 bales off my trailer with the ATV uphill from where I wanted them and roll them with a pitch fork into the barn as they are round after all!
If I was you I would pull them off the truck or trailer with your tractor and use a 3pt spear to move, or get a bigger tractor.
My tractor is basically double the weight, 6' wide and its fine for 4x5's with one on the 3pt, or the HD box blade. But on slight slopes once the bale up 6'+ to put it into a feeder or onto a trailer I go real slow. All the fulltime farmers I deal with seem to have a 6-7-8000lb tractor minimum to do 800lb bales, and then they never have a counter weight on the back.