JohnH, Cartridges of the World has these factory loads:
.358 Win. 200 gr. 2490 fps
.358 Win. 250 gr. 2250 fps
9.3 X 57 232 gr. 2330 fps (handload)
9.3 X 57 286 gr. 2065 fps.
Looks like the .358, compared to the 9.3 X 57, traded off 30 gr. bullet weight to gain 200 fps.