I have towed many different goosneck loads between 15-30k lbs in both single and drw trucks. There really is no comparison. It can be done with a srw truck, but stability and feel is completely different. Under 15k or in a pinch it can be done safely with srw. If you tow regularly over 15k it isn't much of a choice.
Obviously it is silly to talk about total trailer weight when the rawr is what matters, and most fifth wheels over 14k or so overweight the ratings of the rear tires and axle. Losing a rear tire at 60+ with 8k+lbs on the rear of your truck is not fun.