I'll accept that given a good bullet, the .25/06 is acceptable for big game larger than deer out to 300 yards, but IMHO, with the bullets that are available today, it falls short of the 6.5 Swede. The fact that the majority of moose are killed well within 200 yards suggests that laser beam flat trajectories aren't much of an advantage, particularly when one considers the number that have been dumped with .30/30 class rifles. The advantage of the 6.5 over the .257 is not one of bullet diameter, as a difference in diameter of .007" is pretty much meaningless except in mathematical calculations where theoretical advantages appear to be much bigger than they are in reality; but the difference in bullet weight cannot be ignored. Lets look at the available bullets. The heaviest bullet available in the .25/06 weighs 120 grs and that bullet can be driven at 3000 fps from a .25/06. The heaviest 6.5 bullet weighs 160 gr or roughly 33% more. The Swede's velocity is significantly slower, but a muzzle velocity of 2500 has been getting the job done with heavy for caliber bullets in cartridges like the 7X57 and the .303 for more than a century.
Speed has its place in terms of flattening trajectory, but mass combined with speed is what produces momentum, and in game animals that weigh a half ton or so, penetration is what wins the day. Given two expanding bullets of similar construction and weight within caliber, the one with the higher impact velocity tends to have shallower penetration. Taken to the extreme, an expanding big game bullet with an impact velocity of 3000 fps might have a penetration of 12", but reduce the impact velocity to 1600 fps, the lack of expansion results in 4' of penetration.
If you want a varmint rifle that doubles as a good deer cartridge and is still alright for an occasional moose/elk hunt, the .25/06 is probably a top choice. But if the reverse is true, and you want a general purpose big game rifle that can reach out and smack a coyote, the 6.5s are far ahead.
