First off, I don't think the nominal length is comparable between 5th wheels and bumper-pull trailers. I think both are usually measured hitch-to-bumper, and with a 5th wheel that means the body of the trailer would be longer than the nominal length, with a bumper-pull the body is shorter than the nominal length.
Are you planning to live mostly in one place and just move around a couple of times in the year, or not at all? Or are you thinking of only staying a few weeks at a time in any one location and traveling all the time? IMHO a big 5th-wheel would be better while you're parked, especially if you didn't plan to own the same trailer for 20 years.
Now, if you're traveling, an Airstream is an excellent trailer to tow and is well-designed for the purpose of actually traveling. The shape and height of an Airstream make it better to tow, but reduce the space available to store stuff.
A 5th wheel will really demand a premium tow vehicle... and a big one. They're tall and relatively blunt, so they dramatically increase the frontal area you have to push through the wind, and they have a fairly high center of gravity. <EDIT> By that I mean you'll want a 1-ton turbodiesel truck, and for on-road stability you might want a dual-wheel 1-ton.
IMHO, think about how you want to use it. If you're moving every 2 weeks (or more often) I think an Airstream is the way to go. If you're parked for 2 months at a time and want lots of storage and slide-outs, a 5th wheel would probably make you much happier. Try to find a big RV show that has Airstreams (they'll all have big 5th wheels) and tour a bunch of trailers.
Congratulations on the impending retirement, and of course we all hope you'll choose the Airstream lifestyle.