I don't see how you can gow for several days in mountains where weather is changeable and can be wet and get all your stuff and food into less than 5,000 cubic inches. I couldn't. So I'm thinking that maybe a lot of my stuff is really unusually bulky, like fleece doesn't really compress and all the down fills the unused space in my 6,500 inch pack and it seems like its always full even with 20 pounds in it and I like to be warm in camp and I prepare for colder than expected weather. Of course with only 20 pounds I wouldn't stuff anything.
Jim