I own, or have owned, rifles in 9.3x62, 9.3x66, 9.3x64 and 9.3x74.
The 9.3x66 case is only very marginally longer than the 9.3x62, with very little increase in case capacity. The 9.3x62 and 9.3x66 are ballistically about identical. Any claims the 9.3x66 is an equal of the 375 H&H is just...