Hello hoppdoc:
In my humble opinion, for the kind of a soft thin skin of a leopard, a medium speed caliber with close to 200 grains of a soft point bullet of the 8x57, will do a better job than the fast and powerfull .338 when this don´t touch bones.
Needless to say than the 9,3 will also be a terrific choice. even better, I´d say,

I am, althou, on the side of those who still trust a 000 pellets for a leopard charge. You can ear many professionals that it´s a better option to use your rifle, and it´s simply true, but they speak for themselves. Only you know how cool can you keep yourself in such a situation, and how accurate your answer will be.

The only worry I would have when shooting 000 on a charge, would be shooting TOO SOON. Then most of the power of the shell will go directly to the bush and no to the one of spots. But believe me, if you do pull the trigger at the right time, you will see a nice carpet in front of you, even if it weights 160 pounds.

Regards
The Preacher