@RMcDonald7 - Eberlestock is nice stuff - good quality, and durable. Let me start off by saying that I think you'll be happy with that F1 frame and Vapor bag / batwing setup, if you go that route. I have several of their packs, and they are really nice. Be aware, however, that all their packs are made in "Vietnam or Cambodia", not made in the USA. (I wrote their customer service and asked, and that's what they told me.)
@kyler1945 has hunted elk for multiple seasons, and can probably make some good recommendations. I think he prefers the EXO product line, but he can chime in and give you his recommendations. When it comes to what works for elk hunting - listen to him over me. I haven't done an elk hunt.
Here are my thoughts, however: If you're looking for a top-notch modular frame pack, don't overlook the Kifaru line. All Kifaru products are 100% made in the USA, and come with a limited lifetime warranty. Pairing the Kifaru Duplex Lite frame with the bag that best meets your needs would be a purchase you won't regret. And once you have the pack frame, you can buy any other bag later to make it optimal for chasing whitetails or other pursuits if your first bag isn't ideal for that. (I have the 22Mag Gen2 bag and I love it for whitetail hunting.) I don't know if your elk hunt will be archery or long gun, but Kifaru's "gun-bearer" system is excellent. It attaches your long gun to your pack while maintaining the ability to instantly get it into play and shoulder it for a shot.
When you consider that you're 40 now, you'll likely be using whatever you buy for the next 20+ years, so keep that in mind. With that frame of reference, looking at competitive product lines that cost more (even 2X more), the price is less important than getting equipment that will serve your needs the best for the next 20 years. Too many guys buy on the cheap and end up buying replacements or alternatives over and over when they're not fully satisfied with their equipment. In the long run, it costs them MORE.
@JCLINE84 - produced a thoughtful gear dump video last year and it's definitely worth watching before you finalize your decision. You'll want to fast forward right to the 18:34 mark in the video to start right at his discussion on his backpack.