The main advantage is you can run with a non-sliding (less expensive) 5th wheel hitch and not EVER have to worry about smashing the trailer into your cab. And, of course, you can fit full sheets of plywood and drywall in the bed with the gate closed and not look like fool like me with them tilted up resting on the gate.
And, when you're moving your mother-in-law in/out of your house you can make 3 trips to my 4
Truth be told I'd really love to have a long bed but I just do too many grocery runs. The 4X4 thing doesn't change a whole lot that I know of. In my area (Oregon) 95%+ of the trucks are 4X4.
As for the Gooseneck thing, there are a lot of options with newer trucks for attachments w/o bedrails. I just got a 5th wheel hitch with a single cutout between my wheel wells and some rails that go under the bed. Some have a 4 point attachment. I've been researching and reading for months on this stuff and still feel like I know nothing.