kuduae - I do not understand why the smaller 54mm MS case would be loaded to higher speeds than the larger 57mm case. Afterall, the CIP max for the 6.5x54 MS is listed as 53,000psi CIP while the larger cased 6.5x57 is listed as having a maximum working pressure of 57,000PSI CIP.

From experience with Model M98 Mausers, we know the 6.5x57 can easily be loaded to the same maximum useable pressure as a 6MM Remington, 25/06, .270, or even the newer .338/06 which has the same same basic case design and diameter expect for length and if often loaded in the same Model 98 actions), ie: at 63,000psi to 65,000psi.

Perhaps the answer is as simple as the ammo manufacturers never loaded the round to it's CIP maximum, let alone to it's full potential as an experienced handloader could.