It is always interesting to see the opinions of members on this forum.
Defining efficiency or bang for your buck with hard hitting hunting and ringing steel purposes is kind of like saying I want the fastest car with the best gas mileage or the least expensive car that would still be competitive in the race.
Miles per gallon: 280AI and 308 Win. They are not the fastest, but will give you great smiles per gallon return on your investment. It is difficult to take barrel life out of the equation if you are talking about bang for your buck/efficiency.
Agree it is interesting. Many circle track racers need to be both fast and fuel efficient to win. That combination is regularly discussed in aviation too. I think the op clearly defined what was important to him and tried to prevent the thread from veering off topic.
He's looking for something that lies somewhere between best mpg and unlimited fastest. Somewhere between 280/7x57 and 7mm eargonsplitterloudenboomer.
I hear him saying cost isn't a factor. With hunting, that eliminates a build over 10-12lbs all in but not ultra light either, steel means repetitive and higher volume shooting. So recoil management and ease of loading and tuning really stand out to me.
To me that puts us in the area of a modern day 7rm shooting 190+ grain bullets like my 7mm blaser improved or a sherman 7max being at the peak of the curve. 7 rum or 7 mega is on the back side of the curve, 7 saum or 280ai on the front side of the curve.
My bare 7 blaser improved with 24" proof cf and swaro z5bt is 8lbs 4 oz. Backpack mountain hunting to 800-1000 yds and steel 1000+ very confidently. Its taken all antelope deer and elk with 1 shot drt. I have handed it to novices that dont shoot much or over 200yds or ever handled my gun for 400-800 yd shots with the same result with 1 shot. I have done minimal load development in all reality, but have comfortably shot 100rds in an afternoon.
Went to a local competition for the first time recently and started at 1005 yds with 12-15mph crosswind and worked in to 400 yds on 12 targets with maximum of 15 shots and did very well. Most other guys had dedicated bench guns of smaller calibers and had shot the course multiple times and some had notes.
I just dont think your going to do all that with alot of the bigger, faster, but less "efficient" choices.
I could put a better lighter McMillan or K1 stock on and maybe a better but heavier and bulkier turret scope like an x5, if I wanted to double the cost of my setup and maintain that same weight.
If I was to build another the only thing I would change is using a 18-20" barrel and 5-7" can instead of my 24 + 9 setup.