BillK,
Many years ago, I was able to buy a local gunshop's total supply of .321" bullets made for 32 Win. Special ammunition. Since I have "on hand" bullets that were made to expand at about the velocities this class of cartridges usually generate, it is natural that I would use them at either .321" or sized to .318" as appropriate. Since you are starting off "fresh", you should use which ever bullet is to your benefit, cost and/or availability wise. Raimey's generous offer may help with that decision. This applies if you are asking about the 8x58R Sauer & Sohn. The question was for 8x68R Sauer, which I guess was a typo. There is an 8x68S, which is a very good cartridge in the 8mm Remington Magnum class and is only intended for .323" bullets made to expand at a higher velocity.
Have fun,
Mike