VtLuke,
I should qualify my earlier statment about the Astralplane.
Prior to it I carried a Lowe Alpine Contour IV which was my main workhorse for about 11 years. It is 5400 CI plus 900 extension. Before that I had my trusty '74 Eureka Lake Cruiser External Frame Pack - Which is still ocassionally allowed to go out for a trip here and there (squeaking all the way).
The Contour IV always seemed slightly too large in the summer and slightly too small in the winter
which made it perfect if you could only have one pack. It was great for loads under 55 lbs, but not too comfortable for loads greater than that.
Also, 5500 was a pretty good size for carrying gear before the ultralight craze - Whisperlight stoves, stainless steel 2 qt cooksets, 5-6 lb 2 man tents, 3-4 lb sleeping bags and the like. I have since replaced my Contour IV with a lighter Kelty Haiku 4200 CI pack for summer trips with ultralight gear.
I assumed with an 80 lb load you were trail working or heading to Alaska. I can assure you that with today's emphasis on smaller and lighter gear, I would be hardpressed to fill up the Astralplane unless it was with 3 weeks of food - It is even difficult to pack it full in winter, unless I am solo with no one to split gear with.
Then again, if I were 25 years younger with more brawn than backache, I too might want the largest expedition pack I could find to carry off on all those trips I'm was dreaming about.
Seriously, good luck with your backpack!!!