Prosper,
The heaviest .270 bullet commonly found is 160 grs. I haven't seen a 180/.270 in 30 years, and I doubt if there are many left. A 160/.270 has a SD of .297, which is roughly the equivalent to a 200 gr .30 caliber bullet. Yet .30 caliber bullets are commonly found up to 240 grs. The heavier bullet has more core to expand to form a larger frontal area and the larger the frontal area the larger wound volume. Therefore, on very heavy game, the '06 outperforms the .270.
I'd have no problem going after a bear in the willows with a .30/06 loaded with my handloads, but I would not be happy with a .270 in similar circumstances. A big advantage that the '06 has is that its velocity is less prone to result in bullet failure on heavy game. This is the one area where a premium is a good idea in the .30/06, but after having extensively tested premiums for close range performance, I believe 2500 is the limit. The 240 gr Woodleigh has a MV of about 2400 fps from the '06 and is designed to upset fully at the '06's velocity.
The .270 has been touted as a very good long-range medium game cartridge, and it is. But load the '06 with a sleek 150 gr .30 caliber bullet at 3000 fps and it will take care of business with no more gore than the .270's 130 at the same velocity, provided that bullet construction and point the of impact are similar. A .270 loaded with a 150-160 gr bullets can harvest elk and moose effectively and humanely. The same can be said for the .30/06 when loaded with 165-180 gr bullets. .
In terms of trajectory there is no real difference between the .270 and the .30/06. If we use the highest BC bullets and load to equal pressure in both cartridges, it's a wash.
The '06 is certainly cheaper to load than a .300 Winchester. If each round uses 15 grs less powder per cartridge, that's 15,000 grs per 1000, more than 2 pounds of powder in just a couple of months! I don't know about you, but my powder isn't cheap. But while we are on the subject of magnums, even if brass costs the same, I bet I'll get double the reloads from a .30/06 than I would from a .300. I'll get good performance on game with regular bullets where the .300 should use TSX's. The '06 looks cheaper all the time.
I grew up on the '06, and long days at the range ate up great deal of ammo. 100 rounds in a day from prone when I was shooting long range wasn't difficult. I'm not any tougher than anyone else, so if I can do it, and my wife can do it, anyone can. The point I was making about the .460 is that it is specialized. It does one thing particularly well, but because it is so specialized it is not as versatile as a cartridge designed for general purpose. Lesser cartridges are friendlier to shoot than is the '06, but they won't do what the '06 can, and that's why the '06 is special. Yes there is a do everything rifle. A broad range of .30 caliber bullets make that possible, and this range of bullet weights, or more properly this range of sectional density is available in no other caliber. The .308 is nearly as good, but doesn't handle the heavy bullets particularly well. The various .300 magnums and ultra magnums are long-range wonders, but they move the recoil threshold from almost bearable to intolerable. They over drive many bullets structural integrity with MV's at times well over the 3K range.
So the .30/06 can handle game as light as pronghorn to as heavy and dense as buffalo. It can mimic the trajectory of one of our very best long-range cartridges. It can do so economically and with moderate recoil. Sounds pretty versatile, but why is that important? After all, as you say, you could just carry the right tool for the job. Well, one answer to that question is cost. Many hunting rifles are sneaking up to well over $1000.00 and then you have to dump another bucket of cash on a scope, but to me that's not the big reason. The big reason is that you might be holding the wrong specialized rifle at the wrong time. The .257 Weatherby with the 12X scope is just about useless when a whitetail jumps out at 15 yards. The .45/70 is just about useless when the moose appears 350 yards down the power line. Yet under the right conditions, these rifles are better than anything else we might carry, but on those occasions neither is as good as a .30/06 with a fixed 4X scope.