Apparently GoLite has changed the Quest since I purchased mine. The Quest that I use was made in 2007 and has a plastic frame sheet between the back padding and the metal stays. I find it very comfortable but it is also getting pretty badly worn. I am glad to hear your report on the newer Quest; I probably won't get another.

I have looked through the listings of different internal frame packs and have found a lot of them in the 60 liter range but most of them seem to weigh 4+ pounds.

You might want to consider the various packs that use a sleeping pad as part of the load transfer system; most of them come with metal stays that add to the load capacity but only add 3-4 oz. One I can personally recommend is the Six Moons Starlite but there are others such as the Gossamer Gear Mariposa or Gorilla. All of these packs are less than 2 pounds with stays and will handle a maximum of perhaps 35 pounds total with some comfort; they are much better with lighter loads (as is any pack). There is a learning curve with these packs and the learning tends to be personal with a lot of ah-ha! moments.