I had to carry a large ALICE pack in the Army. I found that it pinched my back and caused my legs to tingle. The problem with the ALICE frame is that it is designed to fit the "average" person, probably someone about 5ft 9 or 10. On someone 6ft 2 it rides too high on the back.

The ALICE also hangs far away from the back when loaded, which is undesireable, it makes you feel like you are being pulled backwards.

The mil surplus prices are appealing but if the pack doesn't fit, there is a price to pay in comfort, or lack of comfort. If you think you are going to be carrying the pack for any length of time and distance, you may want to shop around for a good civilian pack. Kelty makes some very comfortable packs that ate reasonably priced, there are other brands as well.

I helps to get out and carry a pack around like on dayhikes. You will see how it rides and condition the body too.