One last time: the 06 case has more capacity that the 308 case. Loaded to the same pressures, the 06 has the ability to push the same bullet at a higher velocity.
Your post contains two errors: 1) you ignore efficiency - case capacity is not the only feature of a case 2) .308 has a higher specified pressure than .30-06. They are not loaded to the same pressure.
And an omission: .30-06 is essentially never loaded with top loads, and as a result the loads can be EXACTLY duplicated with a .308. Same bullet, same velocity.
