Stan, my son. It is good to encounter one who adopts the proper attitude when approaching His Gearness for wisdom and enlightenment. So often its a quick, Hey, GG, I need a pack/shoe/bike. Whassup??" No respect. You, on the other hand, know which side your bread is buttered on.
Camp Muir. Thats a pretty tough hike. For those who arent familiar with it, Camp Muir is the main climbers camp" at the 10,200-foot level of Mount Rainier. Its almost a dead vertical mile from the start point at the Paradise Lodge parking lot to Camp Muir. Four and a half miles, but thats somewhat irrelevant. The worst part of it is that for much of the hike, as one struggles up the seemingly endless Muir Snowfield, you can see the blocky little rectangles that comprise the camps huts.
Anyway, a pack. I agree completely that weight is weight, and the less weight you carry the better. But with packs its a little different equation. If a light pack cant handle the load and begins to collapse around your torso and shoulders, a 40-pound load in a four-pound pack can feel much heavier than the same load in a seven-pound pack. So the suspension counts for a lot. Hence your fondness for the Gregory Whitney ($339; gregorypacks.com), one of the best big-load packs out there, especially for the money.
But these days, pack makers have figured out ways to shave 50 percent of the weight from a pack while keeping 80 percent of the load-carrying capabilitymaybe even better. Thats a big step forward. GoLites Odyssey ($199; golite.com), for instance, weighs three pounds, eight ounces, has a whopping 5,500 cubic inches of capacity, and is rated by GoLite for loads up to 50 pounds. Thats pretty good. I havent had direct experience with that pack, but reports are that it lives up to its billing.
I have used Ospreys Aether 85 ($279; ospreypacks.com), however, and must say I am mightily impressed with it. It can handle 50 pounds pretty easily, and smaller loads extremely well. It weighs in at four pounds, 12 ounces with 5,200 cubic inches of capacity. The added weight comes from a slightly heavier suspension, a few more bells and whistles on the pack, and somewhat beefier fabric. So longevity of the Aether may be better than the GoLite pack. And comfort is great; the hip belt can be heat-molded to your waist for a custom fit.
So, simply based on my own experience, Id go with the Osprey. But find a store that has both it and the GoLite, pack some weight into them, and see what you think.
You may rise now.