Nick Harvey had an 8x68S in a Mauser 66. He used this switch barrel in a standard action, but seated his heavier bullets slightly deeper to do so. He said the velocity loss was only small. If I were doing this, I'd simply experiment with powders until I found the one that (hopefully) minimised or even overcame this velocity loss. Also, just beware that RWS revised at least some of their bullets in this calibre to allow it to be loaded to a shorter length. I have details of that change if you're interested, but off the top of my head I think it was the then new KS range.

With the longer action and normally seated bullets, I have never had any trouble reaching published velocities. That makes it a very easy cartridge to load for using 8mm bullets that were designed for magnum velocities, such as RWS and Speer make.

One of the advantages of the Mauser 66 is that, although the barrel is full length for magnum velocity, the telescoping action and the barrel band sling attachment means the rifle does not sit higher on the shoulder than a standard barrel length Mauser 98. Recoil is also quite acceptable in this flat-shooting cartridge.

I think it might have been the A-Square reloading manual that said that, in in former German African colonies this calibre remains the yardstick, (or 'meter-stick'), by which other cartridges are compared. It's not too hard to see why if used for everything below thick-skinned dangerous game.