this may sound counter-intuative, but too much padding and adjustment!
i have two Berghaus sacs: a 60l 1996 Extrem Guide, and a 30l 1992 Munro. both go to minimal to non-existant effort in trying to make carrying a tent, 4 days food, a rope, a sleeping bag (or, for the Munro, 3Ltrs of water, 2k rounds of 7.62, food and a softie jacket...) and various lumps of sharp metal comfortable to carry, yet oddly both succeed.
i thought about buying one of your new Centurio daysacs (Munro with zips and MOLLE), and i'm sad to say that with a full load, over a hard days effort, i found it less comfortable than my 20 yo munro which has almost as much padding as a pencil case.
i've tried lots of sacs with big loads - Ospreys, POD's, a Lowe Alpine and a foul Karrimor thing with adjustable back lengths, widths, and all manner of crap - and every single time i go back to my Guide, POD Cragsac and Munro. please, please make simple, faffless sacs that just work. shoulder straps, decent belt, big hole at the top, floating (removable?) lid, wand pockets and bits i can attach shock cord to. thats it.