We all have our favorites. Below is a pic of 70 grs of ball powder in several cases.
l-r is the
8x64, .35 Whelen, 9.3x62, .325 WSM, .338 Win, and .375 Mag
All things being equal the case with the largest capacity wins assuming similar diameter, bullet weight etc., and at equal pressures. If you're gonna run one round up to max, gotta run them all to max, and not their stated max but a given max for all rounds, regardless SAAMI, same barrel length etc.
As we can see the .325, 338 mag and .375 hold considerably more powder than the other 3 standard rounds, and thus when loaded to max will outperform the smaller, albeit more efficient rounds, but in the end boiler room is what matters.
In this little exercise the .325 held 84 grs, the .338 held 88.5 grs, the .375 held 97.5 grs and the 9.3 held 75.5 grs. The 8x64 and .35 Whelen usually hold nearly the same depending on brand of case, but less than the others.
Powder was not tapped in more than needed to clear the funnel and tube.