"No doubt, the .35 Whelen is a magnificent cartridge and lots of folks swear by it, but I wouldn't use it to shoot crows."
Maybe so, but it will definitely put them out of the picture!! LOL
Other ways of looking at efficiency include some form of energy per grain of powder, but the one I like is how it hits my pocket book. Cost per shot is a pretty good indicator of "availability for practicing". When I elk hunt with my Persian Carbine 8x57mm, I have the cost of my primer, 50gr of powder, 200gr Nosler Partition, and I throw in my labor. These are reasonably cheap by today's standard as I bought the bullets a "long" time ago. Now, should I opt for my 32WSpl, which took my last elk, I have the same primer cost, I use 32gr of powder, so about a 40% cost reduction, and a cast bullet, which is difficult for me to figure the electricity for the electric pot and the Wheelweights I'm using are still free though labor intensive, so I'll take $5/100. For the sake of discussion, I'll keep the powder and primers at a relative cost of $3/100 for primers and $22/lb for powder. More some places and less at others, probably, anyway. The Noslers were $27/50; so the elk load for the 8x57 comes in at .157 for powder, .03 for primer and .54 for bullet equals $.727 per shot for the 8x57. By contrast, the elk load in the 32WSpl comes to .10 for powder, .03 for primer, .05 for bullet equals $.18 per shot for the 32WSpl. I can figuratively speaking shoot the 32 four times as much as the 8 for the equivalent cost. The 32 is more efficient. H'mmm, but I need to hunt harder, longer to get a decent shot with the 32 as it has a much shorter range than the 8x57. Oh, so the shot is 55cents cheaper, but the cost of the hunt just skyrocketed!!
Efficiency has to be carefully weighed and not taken too narrowly, or we cut off our nose to spite our face. IF a 275 yard shot presented itself on day #1, the 8x57 would prove very efficient to the cost of the hunt, compared to the 32WSpl, which happen to be the two rifles I've personally used for elk. Especially if a 150 yard shot didn't happen for several days or at all. And a step further, if only 400 plus yard shots were available and no amount of stalking could close the gap, a big magnum just became cheap to shoot. Take your choices and make them happen.
It remains a neat discussion.