I'll jump on board with the 5.5-22 NXS. My brother had an 8-32 NXS on his AR-50. He had to get the more inclined base (50 MOA?) to stretch it out. It is counter-intuitive to some to have to go down in magnification to go up in range, but the added internal adjustment you get with the 5.5-22 is well worth it. Plus, you have to put it on 22x with the higher magnification scopes to range with the 2nd Focal Plane reticles anyways.
Speaking of which, if you were planning on doing most of your shooting inside 1500 yards, I would take a good look at the 3.5-15 F1. If I ever get around to doing my 7mm Rem Mag Sendero build, it's the optic I am putting on it. It offers even more internal adjustment than the 5.5-22 and has a First Focal Plane reticle, which allows you to use the ranging feature of the reticle on any magnification.