A 9.3x62 makes a handy bolt action rifle, therefore its increasing popularity. As suitable for a standard length action.

Penetration is determined by sectional density, a formula of calibre (ie frontal area) and weight, plus velocity. Plus of course bullet construction. As calibre increases the bullet weight must increase for the same sectional density.

Not much difference between a .366 and a .375 in calibre size.

Both will perform similarly. But both cartridges can be hot loaded to better performance with modern hand loadings.

For increased penetration in both use the 320 gr .366 and 350 gr .375 Woodleigh bullets.

As Mike says, the .375 is more versatile as it can be used in more countries for dangerous game.

Personally I prefer the .375 Flanged Magnum over the 9.3x74R and the .375 H&H Magnum over the 9.3x62 and 9.3x64 for the same reasons. In theory at least at the moment,