Here are some thoughts by other FAOL members about the subject from this past January. It might help.

http://www.flyanglersonline.com/bb/s...-Pack-opinions

When you go shopping for one, take along a simple list of what you'll carry in it. You can always borrow a couple of fly boxes, etc. at the shops to load into the packs to see how much room is left for the rest of the gear you'd carry. Then try them on for comfort sake..

Another thing I do to all of ours each year. Zip them shut and shoot them with waterproof spray. Not so much for the occasional dunking, but for those long hours of standing in coastal drizzle.
( Wally-world has a WP spray in their camping dept that's effective and haf the price of 3M's Scotchguard product. Don't remember the products name, but you can't miss the can, it's got a big day-glow orange cap on it. ) .

Best, Dave