Winchester, Federal, and Hornady all have loads that are comparable to the 7-08, however Norma has some loads that are quite a bit hotter, as does Brenneke.
If loaded to the same pressures, using the same bullets, the 7x57 will provide a few fps than the 7mm-08. The issue with the Ruger RSI is that you don't have a choice between the 7-08 and 7x57, it is only offered in 243 Win, 7x57, 270 Win, and 30-06.
If you are going to try to make this a long range rifle (only reason I could see the few extra fps between the 7mm-08 or 270 or 7x57) without handloading, try some of the European factory loads or the Hornady Light Magnums.