Nice pants and i wish they had fit better. I am 5-10 135-140 lbs with a runners frame. I found the smallest size waist to be a bit big on me as my waist is tiny. I also found quite a bit of extra material in the rear end area. Nothing crazy but far from the form fitting description most people give this pant.
I was really looking for something slim around the lower leg and that did not bunch at the knee. Although this pant did that better than most they still bunched around the knee, rear end and thigh more than i would like. I was shocked to find out that Patagonia alpine guide pants fit me perfect on the waist, rear end and thigh in comparison. The Patagonia Alpine guide also fit about the same around the lower leg even with the zipper and snap taken into consideration. I also have a pair of Marmot Rock Star pants and although even a bit lighter than the LT pant they are much more form fitting and slim than either the Arcteryx Gamma Lt or the Patagonia Alpine Guide pant.
If you are not built like a girl and want a pant that is form fitting my guess is these would be just the ticket. If you are built like a girl with 26-28' waist and tooth pic runner legs i would go with the Guide Pants or Rock Star.