The old military ruck didn't have a hip belt (ya I know I am dating myself) with my redwing 3100, the pack hip belt kinda rides right on top of the upper part of the web belt. By the time I am all cinched in, nothing moves. It takes a little while to get used to things at first, but then its all good. It feels better with a load then it does empty. My lbe has two canteens sandwiching a folded up and folded over the belt poncho secured by blousing rubbers in the small of my back, several odd pouches clipped around the belt, and two 30rd m16 mag pouches with the seperators clipped out and an expander sewn in so they can hold a pelican 1030 case in each one. When I am only going out for a day or so (sometimes a few if I am feeling spry) I ditch the main pack entirely, and attach a mil surplus butt pack to the lbe and go like that. What I suggest you do is find a willing army surplus store to let you set up a set of lbe, bring in your pack, and try everything on with a little bit of load (sandbags or free weights will give you an idea even if they aren't as comfortable as the properly loaded bags will be). I have set up a couple friends this way, and they love the flexability, a couple of other friends have tried my stuff on and say "how the hell do you walk in that crap"
Try before you buy. If you are in the denver colorado, or the spokane washington area, I could give you some idea as to where to go otherwise, I am of no help in that department. Hope this helps a little.