I've made a G4 pack, and as I don't like the Z-Rest, which it uses for a "frame," I'll be hacking on it.

This particular pack was intended as a prototype, starting off stock and to be cut and resewn as needed to meet my own idiosyncracies, of which, being human, there are many. When finally satisfactory, I'll make a final one.

My question is has anyone made changes to the G4 design that's worked out well for them? And if so, what?

I carry a G-4 pack but I bought it complete. I've lightened my load so much I've been considering adding some kind of compreshion device. I need to shift the load/weight higher now but I also want to be able to use it for light bulky cold weather gear also.