The G4 is one of Glen Van Peski's origonal designs. This is an OLD design as far as backpacks go. I believe you can get a pattern for it from Outdoors Wilderness Fabric's.
Both are good packs, but I find them way too big for what I need. I use a Miniposa from about 6-7 years ago for longer trips. The Murmur works for up to two weeks, though it is overloaded...the harness is OK...the new buckles suck when coupled with the herringbone pattern straps. The unique feature on most of Gossamer Gear packs used to be the pad pouch mounted outside the pack. Many manufacturors offer this, or, some varrient of this, nowdays. I use a 5 piece NightLite pad, cut and taped, that fits into the pouches, and, supplys a frame good for 25-30 pounds.
As with most light gear, they are not real durrable. The Kumo is a beefed up version of the Murmur. Most will last about 60 days on the trail without any repairs, but plan on some repairs if you overload them, or wish to use them for longer. Usually, most UL gear is good for 60-80 nights on the trail. UL gear from GG is no different.
Anyway, the G4 (and G5) is massive! It will hold most anything you need for a month out! Weight limits are the big restriction, not volume. I usually took my older GVP G4 (second hand) out when I loaded for family canoe trips. Tent, Tarp, cloths and extra cloths, food and extra food...over 30 pounds. It held up well but I gave it away to a partner last year. I never used it.
I typically hike/paddle the ADK's.