I've had 1500lbs of steel in the bed of my 2004 F150, no problem. The newer ones I think are rated for more than that.
Sho nuff Tex, WHB, stick to standard 4'X5' round bales and you wont have any trouble, place a 'push pallet' in the front floor of your bed, if you unload with a bale spike on a tractor front end loader you wont crush the bed or break your back glass.
