The Mega Cab is only offered with the short bed. Looking at the specs, you
will gain 20" back seat room over the quad cab w/no sacrifice in the
length of the box. (There's also some storage space added behind the back
seat so the added 20" isn't all legroom). The wheelbase is 20" longer.
What this means is the mega-cab truck, bumper-to-bumper, is 4" short of
being 21' long. That means it won't fit in my garage. Prolly won't fit in
quite a few others, either, especially if you put a brush guard (Urban Car
Catcher) on the front and have a big ugly hitch ball (Urban Tailgater's
Radiator Punch) sticking out the back. In this neighborhood you park a
fine ride like this on the street or outside in your driveway and you risk
getting vandalized or broken into (if not stolen) once a year or so.