How much weight on gooseneck/5th wheel/truck bed?

Keep in mind the horses add almost nothing to the hitch weight, as they ride over the axles. The only items that will add to the hitch is what you add to the living quarters. The only about half or less will go to the hitch.
My daughter uses my 2001 Ram 4X4 Cummins to pull a two horse slant, no issues. I pull a 5er that comes in at 11,000# with a GVWR of 12,320#.
All that said it is your choice to tow over your TV's GVWR, but many do it with 250/2500's without issue.