nsaquam,
The only problem with your comparison is that there are just about as many sources that credit the .30-06 220 with 2600 fps. Nosler's manual, for instance, lists 2602 for the 220 .30-06--and that's sticking to the SAAMI pressure maximum for the .30-06. In my experience it's easy to get 2650 or so out of a 220 in a 24" barreled .30-06.
Plus, many shooters think that roundnose bullets drop like a rock. The Nosler 220 Partition, however, has a BC of about .350, which in my experience is pretty close to reality. Plus, out to 300-400 yards muzzle velocity has a greater effect on trajectory than BC.
Let's compare a 220 .30 Partition and a 250 .338 Partition, both started at 2600 fps. Sight them both in 2" high at 100 and they're both close to dead-on at 200. At 300 the .338 is an inch or two lower than the .30 caliber, and at 400 around 4-5" lower. This doesn't amount to any practical difference in the field.
Yeah, you've got another 30 grains of bullet weight in the .338, but penetration will be similar. In fact I'd bet the .30 220 would win a penetration contest. It wouldn't be by much, but then 30 grains (and 1/32nd of an inch in diameter) isn't much either.
If somebody already has a .30 caliber of whatever variety, I haven't found all that much difference in going up to .338. This is based on plenty of experience with the .30-06, several .300 magnums, the .338-06 and the .338 Winchester Magnum. I'm not even all the sure that going up to .35 or 9.3 makes all that much difference, 95% of the time.
The reasons most hunters see some difference in field performance between, say, a .30-06 and a .35 Whelen are (1) they tend to use 180's, at most, in a .30-06, and (2) they're easily convinced by one or two animals that there is a real difference. Otherwise why did they buy a "bigger" rifle?
But if they simply loaded 220's (or even 200's) in a .30-06 they would probably be amazed at what it can do. However, there's no real fun in simply buying another box of bullets instead of another rifle, especially when we can make believe that the new rifle is A Really Big Rifle.
Unless you're one of those hunters who simply has to have a rifle to fill every little gap in the picket fence (which sort of resembles me) it makes more sense to step up significantly in bullet diameter and weight. To me that means 9.3x62--or a .375 H&H.
