Fifth Wheel or Goose Neck

Beyond the question of frame stress there are other issues to consider as well. You mentioned having a clear bed. Depending on how often an open bed is needed, then just remove the fifth wheel hitch or leave it hanging on the kin pin when you unhook. There are plenty of under-the-bed mounts that will leave the bed totally open with the hitch removed. But the other big difference is ease of alignment. From the driver's seat, the fifth wheel hitch is visible, left-right alignment can be off several inches and fore-aft alignment is not an issue and you can hitch up with the jaws open or closed with most hitches. OTOH, a floor mounted ball is not visible from the driver's seat and needs to be aligned both left-right and fore-aft within less than an inch. Safety chains are required for ball mounts. All things to consider.