I've owned these for a while now along with the Rampart pants. I'm 6'4" with a 36" waist and the 36L is a good fit. I prefer the Rampart pants to these because these are just a little tight fitting in the thighs, and I've by no means got thunder thighs. I am a skinny dude. They're still comfortable, breathable, a little stretchy, and look good on the trail as well as around town. I like the Rampart more due to them having more pockets and have a little more of a relaxed fit. The Perimeter is still a great pant, but I prefer the Rampart to them.
First pair of Arcteryx pants I've purchased. Fit OK out of the box, took them on a trip to Africa and they worked fine, zippered pocket is great. However, brought them back and washed them, now they don't fit at all (waist and in). I generally wear 32-33 in Patagonia if that's any help, a 32 in these is way small for me.