Phenix Quads work fine. I'm caloricly challenged and I still have extra slack in the straps. Be careful though because Phenix came out with some smaller straps. I think they called them Phenix .8 straps? I must say I liked them better though. They moved the bag further up on my back and there isn't as much of a gap between the top of my bag and my back. I'd try both if you can.
I just bought the new quad shock. Minor changes, but fit and feel great. They even make a modle with a chest strap, but I thought better of that. Since you are always taking them off or putting them on.