As most people know, 7x57 factory ammo is deliberately loaded down to safeguard against use in ancient ex-military rifles. Handloaded to the same pressures as the 7-08 (which is fine in a strong, modern rifle), the 7x57 will - slightly - beat the 7-08: not a surprise, since the case capacity is greater. But that slight edge doesn't really matter to the game being targeted.
One real plus is that the 7x57's case allows the use of longer bullets. Of course, the downside is that the 7-08 can be built on short actions, which the 7x57 is generally too long for (
some manufacturers' short actions are long enough; most are not). And it could be argued that if you really need the bigger bullet, you're better off with a .30-06 or equivalent.
Practically speaking, the 7x57 and 7-08 are essentially equal. The only real difference is that the 7x57 is a 'classic' cartridge, whereas the 7-08 is a relative newbie without much history (to the best of my knowledge, neither W.D.M. Bell nor anyone else has ever used it on elephant!). I just like the 7x57. See Jack O'Connor's article, "Forty Years with the Little 7mm", and perhaps you will be hooked too!
To me, a Manlinchler style rifle (a real classic) should be blue steel. I'm sorry, that's just how I feel.
No need to apologize ... we are all entitled to our own opinions / tastes.
IMO, a true Mannlicher-style rifle should have a butterknife bolt handle, a rotary magazine, and double-set triggers. And of course it should be chambered in 6.5x54. But that's just me.
