Jim,
I'd first recommend the Kifaru followed closely by Mystery Ranch. Like so many things fit is personal. There are things I like a lot about both systems but personally I give the nod to the Kifaru packs.
Having been hauling heavy loads in Alaska since the mid-70's with everything from external aluminum frame packs to internal frame packs my opinion is based on having been there and done that. BY FAR the best system I've found is either the Kifaru or Mystery Ranch. For what it's worth I am currently using my 5th or 6th Kifaru pack (their Longhunter guide model which isn't being made any more) and also own and sometimes use a MR NICE 6500 and a MR Metcalf.
For most hunting situations I think a simple big bag with good compression straps is the way to go. You can always make a big bag smaller by compressing it down but you can't make a small bag bigger. The weight differential between a small bag on a removable frame versus a big bag on a removable frame is negligible.
There are two things upon which you should not compromise: one is the presence of a mid-level support platform/sleeping bag compartment. You don't want a heavy load resting in the bottom of a bag. The bottom of a heavy load is best carried with it bottomed out around your waist. The second is an excellent load lifting system to keep the weight off of your shoulders and on your hips where it belongs.
Hauling September 2013:
The benefits of having a removable frame: