I doubt the 8.5x63 can replace the 8x68, as this cartridge is based on the .280Remington. It can ofcouse shoot the heavy 300grain bullet to duplicate the .333Jeffery. As a cartridge this caliber has more versatillity than a hot magnum.
The 8x68S can be loaded to get the 900M/sec with the 14,7gram bullet, and 930 M/sec with a 12,8gram bullet.

Looking foreward to see the upcomming M03

.

If i were to start all over with a repeter, it should also become the M03 in 6,5 & 8 X68 + the 9.3x70Magnum. Nur deutsche kaliberen...