when looking at the big picture, there isnt much difference between the 144-153 sleds. 144 to 153 is 9" of track (three pitches with a 3" pitch track). on the rails, it is only
4.5" total. you have to decide for yourself if you want the extra length for cross country and back country/hillclimbing.
i personally would buy the sled for the steepest and deepest i would ride, and then live with what i have for the flat areas. hate to go to the steep and deep and not truely be able to ride where i want to without alot of effort with the shorter track.
also you need to look at how much it is going to cost you in mods (tunnel protectors out, new drivers, new track cost, labor ect..) to install a really tall lug into the xtx. i dont think you can go over 1.75" without drivers in the xtx but, dont hold me to that. then for you to want to go 16" wide, you will have more obstacles to conquer in the tunnel width dept.
again it appears you are better off with the mtx for your application. just my .02 ski