The 7mm-08 only has slightly less powder capacity than the 7x57--about a couple of grains, which amounts to about 4% less. This means the 7x57 is (at least theoretically) capable of about 1% more muzzle velocity with the same bullet at the same pressure.
This is pretty much what different rounds of the same load will vary in velocity--so the 7mm-08 and 7x57 are pretty much the same thing. I have owned a couple of 7mm-08's and, using published data, really couldn't see any difference between the 7mm-08 and the 7x57. One load that really shot well--50 grains of IMR4350 and the 139 Hornady Spire Point--got over 2900 from a 22" barrel, right in line with Hodgdon's data, where I got the load. It is also no trick to get well over 2500 with a 175 from the 7mm-08, so anybody claiming it is less cartridge than the 7x57 is cuting things pretty fine.
Actually, even with factory loads the 7x57 doesn't come off too badly in comparison with the 7mm-08. A few years ago I chronographed several 7mm-08 140-grain factory loads in a 22" barreled Remington Mountain Rifle and none ran any faster than 2750 fps. More recently I chronographed 3 different 140-145 grain 7x57 factory loads in the 21" barrel of my 7x57 Serengeti, all advertised at 2650 fps or so. All at least matched that, and the Federal Premium load with 140 Partitiions broke 2700. So there isn't as much difference as the ammo catalogs would have us believe. Plus, there is still a 175-grain RN factory load available for the 7x57 (Federal), and nothing like that for the 7mm-08.
The fastest factory load I've ever chronographed in the 7x57 was indeed the Hornady Light Magnum, when they loaded it with the 139 Spire Point boattail (now it uses the 139 SST). In the 24" barrel of another custom rifle with a short throat, it went around 2950! Accuracy was very good too. But in most 22" barrels, with more normal throats, it doesn't beat the "standard" 140-145 grain stuff from Remington, Federal or Winchester by much.
I see somebody brought up the 10,000 mooses thread. Well, the biggest animal I have ever taken with the 7x57 was a bull moose in Alberta, with a 41" spread. Not the biggest moose in the world, but not the smallest either! it has also worked fine on wildebeest in Africa, and out to almost 400 yards on springbok and pronghorn. Not bad for a 115-year-old cartridge!
