I had a small load on my tandem dually gooseneck today and towed it 300 miles and over a couple mountain passes. My gross combined weight was just under 22000 lbs. While I was driving I was thinking “at this weight I don’t think I would know anything is behind me without looking in the mirrors.” I think the new Ford F-350 SRW 7.3 would handle a 16000 lb trailer extremely well. That said, for the occasional camping that my wife and I do we have absolutely no desire for anything larger than our 36’ fiver. Although we do sometimes haul a motorcycle on the back of the fifth wheel.
Edit: I guess I should point out that I have the Powerstroke so I seldom see over 1500 rpm and almost never over 2000 rpm with that kind of load. I would hope your expecting the 7.3 will need to rev a little to make power.