The 9.3x62 necked down would be a ballistic twin to the 6.5-06, 6.5 Rem Mag, 6.5x284, and not near a 264 Win Mag. And the 6.5x64 Brenneke is the European 6.5-06; it uses .270 Win brass as a base so the brass is 64mm in length. No where near the capactiy of a 9.3x64 Brenneke.
And the 7x64 Brenneke is the original 7mm Mag. They loved that cartridge with long bullets in Africa in the early 20th century.