I pulled the all data from the Hodgdon loads for 150, 165, 180 and 200 grainers.

The average velocities of the 4 bullet weights and for all listed maximum loads each bullet weight

300 Win........ 2988
300 Wby....... 3055
300 RUM........3158
30-378..........3362

The average all 4 bullet weights with load that gave highest velocity

300 Win........ 3109
300 Wby....... 3208
300 RUM........3323
30-378..........3484