I used to own an Ark 09 version and though it didn't work for me, I think it is still a good pack. My size Large was under 16oz, but the torso wasn't quite long enough for me (I am 21.5"), and I had problems getting water bottles out of the side pockets with the pack on as they came up pretty high. Now, that may just be me and my lack of flexibility so YMMV. I also wasn't a huge fan of the wing style hipbelt and prefer wider/longer "wings" even if they have little to no padding. That being said the pack just oozed quality and the sewing was immaculate.
I went to the SMD Swift '10 (sewn on hipbelt, before the stay) and it was almost identical in size as the Ark despite what the SMD website says (Its a BIG pack). I liked this pack much better, but admittedly the sewing is not as good. Mine bit the dust after 1300 miles. Like I said mine had the sewn on hipbelt and no stay but after a little trimming, it was down to 16.4oz. The hipbelt pockets are nice and big as well.
I also have an older 2008 GG Mariposia Plus (with the old CF stays) and it is a smaller pack than the other two, but overall carries well. The wide shoulder straps are a bit odd, but worked for me as long as I wore a sternum strap (I don't with any of my other packs). The new ones look nice, but I have no experience.