The 30-06 cartridge is a great case, it just needs optimized. For hunting killing is the goal, for most going to a 300 mag of any kind is simply penetrating it quicker. My thinking is, anytime you don't stop a cartridge in the game animal your using it on, your simply throwing energy away, that should have been transferred to that animal.
NOW, make no mistake, I no better than to confuse target shooting from Hunting, neither one has anything to do with the other, unless you don't want the most efficient for that job. but one is not well suited to the other!!
I am building what I have thought long and hard about. trying to build one gun to be the most efficient for anything from Antelope to the largest most dangerous game on this continent. I want to be able to shoot flat enough for antelope and deer size game out to 600 yards, But I want to be able to use it with a heavy enough bullet to stop the largest and most dangerous animals at reasonable ranges they are hunted at, and still be able to stop any dangerous threat inside 50 yards if my life depends on it.
I Narrowed it to one cartridge, the original 30-06 cartridge. It has been necked up and down, blown out and shortened in about every caliber we can think of. I chose between to calibers,, 338, and 358. I feel both would do what I was trying to do. One more suited to longer range and smaller game, while still quite capable on the larger game. the 338. Yes a 280 AI would be better for long range and smaller to medium game, but in my opinion, not a good choice for the largest most dangerous game even at close range.
I chose it over the 35 Wheelan that I feel is not quite as good for smaller game and longer range, but better at the largest game. I feel both of these calibers in this case are the most versatile of any caliber it has been chambered to. There are better choices in maybe 375 or 400 caliber for the most dangerous game at close range, but not at all a reasonable choice for smaller game especially at long range.
So in my long winded way of saying it, I chose the 338 knowing that at my age it would see more use on antelope and deer sized game. But if the opportunity to ever hunt moose or Brown Bear, it would be adequate. I also wanted to be able to build a rifle light enough that at my age I still would want to carry it all day, while keeping it light enough, yet still not beat me to badly when I do need it for either task.
But I would build a 30-06 today, before I built a 300 mag in any case. In fact if nothing but the largest most dangerous game was all I cared about, I'd have built a 45/70 #1 Ruger, over any magnum as well. I just don't see anything they do any better. But make more noise, and beat you up more. JMO