Went through all this logic for the past year or two...
I've been selecting 1 rifle/1 pistol for my stable (possibly a rimfire or shotgun to complete the set), and have researched the livid DAYLIGHTS out of everything based on the OP's question.
I settled on .30-06. I reload, so I can go from groundhog to grizzly with it. While .308 Win may take it in competitive gilt-edged precision (which, IMHO, has more has to do with platform and recoil control than cartridge), the .30-06 has that extra edge in power and penetration. I can cross-load .308 Win-> .30-06, but not the other way. It's got 110 years of reloading knowledge to it. Also, it's EXTREMELY common - as others said - it was available when the .308 wasn't.
I've looked into .45-70, .30-30, .308, 6.5x55 (and .260/6.5CM), 7-08/7x57/7RM, and 7.62x54R. Disqualifiers for each:
.45-70 - VERY hungry cartridge in lead/bullet cost (either cast or jacketed), poor trajectory, and not easy to make a light-recoiling shot.
.30-30 - tops out at ~200yds. .308 can do same tricks, but handle spitzers better.
.308 - Can do .30-06, but can't keep up past 180gr, can't push long VLD's as fast as .30-06. Smaller case-capacity makes it friendlier to subsonic and .30-30-like loads though.
6.5x55/.264-range - my old Love. However, she was very fussy about equipment needs (can't find reloading components or tools locally, can't use components from other sources, has fast-twist so poor with practical cast-shooting).
.284-series - EXCELLENT ballistics, but peaks out at .310 SD (175gr), only a few molds for cast-shooting, doesn't have the weight-capabilities that .30-06 does.
7.62x54R - PROLIFIC surplus ammo, but poor hunting ammo support. Needs .311 bullets (not as common), unsure of cast-capability (less molds to choose from), and most spare cases are made of steel with corrosive primers. I don't want to have to find a stream in the field to rinse my barrel with.
Honorables - .375 H&H, .35 Whelen, .358 Win - the .375, while capable of killing ANYTHING, has a heavy recoil for factory loads, eats powder, and eats more lead per-shot than the '06. The .35's are the most EFFICIENT (grain/powder to muzzle-energy) category - but suffer heavy recoil if trying to propel them long-range, and they don't have the B.C's of .308 cartridges. On a plus- I can use my .357 bullets in a .35 rifle in a pinch.
ALSO - .30-06 and .357/.38 run the same general weights of bullets - so casting is a bit more comparable.
FWIW, though, as this is all theory and concept - those with experience feel free to debunk me with reality.
I've been selecting 1 rifle/1 pistol for my stable (possibly a rimfire or shotgun to complete the set), and have researched the livid DAYLIGHTS out of everything based on the OP's question.
I settled on .30-06. I reload, so I can go from groundhog to grizzly with it. While .308 Win may take it in competitive gilt-edged precision (which, IMHO, has more has to do with platform and recoil control than cartridge), the .30-06 has that extra edge in power and penetration. I can cross-load .308 Win-> .30-06, but not the other way. It's got 110 years of reloading knowledge to it. Also, it's EXTREMELY common - as others said - it was available when the .308 wasn't.
I've looked into .45-70, .30-30, .308, 6.5x55 (and .260/6.5CM), 7-08/7x57/7RM, and 7.62x54R. Disqualifiers for each:
.45-70 - VERY hungry cartridge in lead/bullet cost (either cast or jacketed), poor trajectory, and not easy to make a light-recoiling shot.
.30-30 - tops out at ~200yds. .308 can do same tricks, but handle spitzers better.
.308 - Can do .30-06, but can't keep up past 180gr, can't push long VLD's as fast as .30-06. Smaller case-capacity makes it friendlier to subsonic and .30-30-like loads though.
6.5x55/.264-range - my old Love. However, she was very fussy about equipment needs (can't find reloading components or tools locally, can't use components from other sources, has fast-twist so poor with practical cast-shooting).
.284-series - EXCELLENT ballistics, but peaks out at .310 SD (175gr), only a few molds for cast-shooting, doesn't have the weight-capabilities that .30-06 does.
7.62x54R - PROLIFIC surplus ammo, but poor hunting ammo support. Needs .311 bullets (not as common), unsure of cast-capability (less molds to choose from), and most spare cases are made of steel with corrosive primers. I don't want to have to find a stream in the field to rinse my barrel with.
Honorables - .375 H&H, .35 Whelen, .358 Win - the .375, while capable of killing ANYTHING, has a heavy recoil for factory loads, eats powder, and eats more lead per-shot than the '06. The .35's are the most EFFICIENT (grain/powder to muzzle-energy) category - but suffer heavy recoil if trying to propel them long-range, and they don't have the B.C's of .308 cartridges. On a plus- I can use my .357 bullets in a .35 rifle in a pinch.
ALSO - .30-06 and .357/.38 run the same general weights of bullets - so casting is a bit more comparable.
FWIW, though, as this is all theory and concept - those with experience feel free to debunk me with reality.