I have a Mauser K98k that the Israelis converted to 7.62 Nato. They put a spacer in the magazine box to accomodate the shorter cartridge. Although it does function reliably, the feeding is not as smooth as with the original cartridge.
The things that a .308 will do that an 8x57 will not pretty much boil down to the use of .308 diameter bullets. Other than that, they are functionally equal, with the 8x57 having an edge in power if loaded to its potential.
