Some imagine the 7x57 to be a "weak sister" compared with the 270. It's not necessarily so. Nor is the 270 anything like being under powered. Both are excellent chamberings.
130 grain comparisons
Remington Scirocco 270 ammunition,130 grain bullet, 3060 FPS.
270 loaded with 56.6 grains H4350, 3157 FPS @ 61107 PSI, 26.7% efficiency.
7x57 (per QuickLoad) loaded with 130 grain bullet and 51.5 grains H4350, 3120 FPS @62900 PSI, 28.6% efficiency.
Hodgdon does show a very zippy StaBALL 270 load, but I don't have a way to compare that powder's performance in the 7x57. Maybe someone can contribute that information.
Conclusion: At this bullet weight, both 270 and 7x57 reloads beat Remington commercial 270 ammo. 270 reloads have a slight advantage vs 7x57, but not much. The 7x57 is slightly more efficient at converting powder to MV.
160 grain comparisons
Best 270 load from the Hodgdon site, 160 grain bullet with IMR 7977, 2843 FPS @ 59800 PSI.
7x57 QuickLoad estimate, 52 grains Ramshot Hunter, 2837 FPS @ 59832 PSI.
Efficiency difference seems to disappear with 160 grain bullets.
Conclusion: Not enough difference to really distinguish one cartridge from the other.
Note
I run my own 7x57 at 2750 FPS, and a few thousand less PSI than the 160 grain QuickLoad estimate.
So if you have a 7x57, you don't need a 270, and if you have a 270 you don't need a 7x57. The differences are the stuff of which pointless arguments are made.
Of course, the 7x57 is a much cooler cartridge.....