I own both the kanab and gila pant. If you are looking for an extremely light weight early season pant you will be hard pressed to find a better one. As far as the difference between the two is pretty hard to tell. The stitching in the kanab pant is not as tight as the gila pant which results in a little more "itchy" feeling against bare skin. With that said, you will be hard pressed to find a wool pant that has tighter stitching as either of the first lite pants.
As far as size is concerned, yes it is whacked. Call them on the phone and they will tell you as much. I typically wear a 32 waste and a 34 to 36 length pant, the XL size in the first lite is very close to a 32 waste and a 34 length. The leg cut is closer to a taper cut rather than a boot cut.
The stitching is tight enough to provide pretty good wind protection, and when coupled with a base layer they provide pretty good insulation.
I have owned Sitka ascents pants and tried the KUIU attack pants, really did not care for either one, the first lite pants are my pick of the other two mentioned.