Having carried meat in the main bag and in a load shelf I would say that there is virtually no difference, especially if you let your meat hang for a day or so. Packing out 50-80 lb of meat with 3-4 days of gear (50lbs) is doable in a 3500-5000 ci bag with meat shelf. With larger bags once your bag is full of gear and your shelf is full of meat you have a difficult situation where even with load lifters your bag will sag and not be in an idea spot for heading back down the mountain so I wouldn’t run a 6000-8000 ci bag with a meat shelf.
Having a bag that is the lightest will be one with a main bag and not much else. Organization bags with pockets, zippers, etc add weight.
I don’t think you can go wrong with kifaru, stone glacier or exo. It’s just personal preference, fit and style. I don’t include MR because they aren’t American made anymore.
My personal all time favorite bag is a MR crew cab, it has bat wings that held gear and a main bag that would hold some items with a center shelf for meat or gear.
I currently have a couple different Kifaru frames and bags depending on how and what I’m going to hunt.