Re: .30-06 and .308 Win?
Using Logic, the .308 was designed to be fired in a short action military rifle.
It was designed to replace the 30-06, because a soldier could carry more ammo if the ammo was smaller.
If comparing 150 gr bullets / rounds, the .308 is about 150 fps. slower than the '06.
The .308 is not designed to shoot 165 or 180 gr bullets.
To get the velocity, Winchester designed the .308 to use a different powder than the IMR 4350. Although you can use either the 4350 or 4320 if you had to!
Dad used IMR 3031 - but you could also use 4064, but you can't trick it to shoot heavier bullets and retain accuracy - the same as a 30-06 Springfield.
You didn't say what you wished to hunt with it.
Deer - 150 gr is all the bullet you need!
Bear - I wouldn't mind using something a little heavier - especially if the hunter was inexperienced.
My .300 Winchester Magnum and 180 gr Sierra's is more suitable for hunting bear then my 30-06, although both will do the same job. Just that I won't have to sight my .300 Winchester Magnum in twice to use it for both seasons.
The old saying - you have to dance with who brung you - is oh so true when it comes to hunting bears.