I'm no super trooper but I got an Eagle Large Becker recently and used it on an overnight backpacking trip on turkey weekend. Worked great! I really like how the attach loops and straps everywhere work. The pole loops on the side worked well to hold my SKS bayonets (AKA indestructible tent stakes).
The Large Becker is like 2400 ci in the main compartment and around 2900 ci total including the external pouches. This is favorable to a moderate outing. On a mega-trip maybe the bigger packs from 3500 to 5500 ci might be better. I'll tell you right now this tenderfoot didn't want to carry more than what I could load in the Large Becker. More below, though.
This is by no means a fighting setup, but I attached 2 x SAW ammo pouches to the hip belt and put 2 qt canteens in them. (the waist belt has attach loops) Also, an Eagle recon butt pack on the front with food and some other stuff. Makes me look like I'm carrying a papoose or something. I'll admit right now I carried too much food and probably too much water (2 1/2 gallons) but hey, some safety margin for those E&E days, right?
There is no 1st/2nd/3rd line setup in my current rig. It's an all or nothing setup.
I did not use the internal frame (I haven't got one yet)
Does that help?