I'm not Texas Camper, but here's my 2c what it's worth...
From what I've read through much googling and the desire to separate the wheat from the chaff concerning wheelbase and towing, TV wheelbase is not such a big factor for towing TMs. The links I've come across with any math or analysis backing them up point squarely to wheelbase being important for sway control (and weight distribution being important for emergency handling). The rules of thumb like "110 inches of wheelbase for a 20ft trailer, plus 4" wheelbase for each additional foot" are based on wind forces acting on the large surface area of the sides of a regular full height trailer and causing sway, so don't apply in the same way to a TM which inherently resists sway and has half the surface area of a regular trailer. Other links suggest that manufacturer's tow capacity figures already account for any lever effects involving trailer weight, wheelbase and overhang (rear axle to tow coupler distance). Of course tires, suspension and other factors are all part of the equation, too.
If you had a 3500lb tow rated TV then I think the 2619 vs 3023 decision would be important. But with a 5000lb tow rating IMHO I don't think it matters - you're going to have either a 750lb margin for one TM or a 1000lb margin for the other. Just load lightly and definitely use a WDH.
Of course with an Xterra, with both TMs it will be slow for the steep grades/high elevations. But whether to change the TV for a V8, long wheelbase, full-size pickup is a different decision involving other factors.
Have you seen this thread?:
http://www.trailmanorowners.com/foru...ghlight=xterra
Paul