Hi Bonk,
The main thing about 9,3x62 vs. 9,3x64, as the one between 7x57 vs. 7x64, is:
Will be used factory or handloaded cartridges?
I have had both 7x57 and 7x64. In a Mauser 98 with a standard CIP barrel, and with its magazine lenght, the OAL of the 7x57 can be a lot longer. So, the velocity...