The Leopard should be one of the easiest shots on any safari and you don't need a lot of firepower for it. A lot of people get very technical about calibres - but if the bullet gets put in the right place on the first shot the cat won't know the difference between a 30.06 and any other calibre. I'd suggest a 30 of some kind with a fast expanding bullet such as a winchester silvertip. Top the rifle off with a good scope with good light gathering capability and QD mounts. If you have to do a follow up take the scope off and leave it in the blind or in the truck.

Before you go into the blind, check the exact range from blind to bait and zero your rifle to that EXACT range...... your PH should make you do this anyway.

I don't like shotguns for follow ups at all - but that's just a personal opinion. FWIW I did a follow up last year on a Leopard with another PH who works for us. He used a 12 gauge and I used my trusty .500 We got charged at close range and both whacked the cat in the face at 6 yards. The rifle bullet travelled the length of the cat and exited and killed him. The 12 gauge didn't even penetrate the skull - although it did'nt do his dental work any good.