In a strong, modern rifle, the 7x57 has a slight edge over the 7mm08 but it's slim until bullets weigh over 150 grains. Similar to the ballistics comparison of the 6mm Rem and 243 Win(same cases, diff caliber).
I have rifles in both cartridges and they are basically the same with medium game type bullets. I second the idea of using the 7x57 in Mausers since their mag and feed lips are designed for this cartridge size/shape.
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