The 12/12 9.3x74R drilling like Merkel, Sauer, or similar European combos is a classic and highly regarded setup for leopard follow ups in Africa tons of PHs and hunters run similar configs 12/12/9.3x74R exactly for wounded cat work or bushbuck medium game backup.
9.3x74R 286gr softnose or solid at 2400 fps has plenty of punch for leopard deep penetration, good expansion on vitals, handles bushbuck easily, and it's legal minimum in most areas for DG backup.
Twin 12 gauge barrels Brenneke slugs preferred give instant follow up shots without cycling huge edge on a charging leaping cat in thick stuff faster than bolt or double rifle reload.
Versatile slugs for close urgent, birdshot for plains game or birds if needed.
Balanced, quick handling gun short barrels keep it maneuverable in bush.
Aimpoint Micro H-1/H-2 on it? Super fast target acquisition paste the 2 MOA dot and go, parallax free, both eyes open for snap shots, bombproof military grade, low weight, long battery 50k hours. Many hunters mount am on drillings doubles for dangerous game big win in low light dense cover or when adrenaline hits. Some purists hate optics on classics aesthetic, weight on barrel rib, and mounting needs a solid base drill tap rib or use clamp on. Dot can bloom in bright sun if not adjusted, but modern Micros handle it well.
Pure double rifle .375 H&H or .416 Rigby for pure stopping power but slower second shot).
Bolt action .375/.416 with quick-detach scope more accurate at distance but slower cycle.
Pump slug gun Win M12 12ga as backup fast follow ups, cheap.
But for combo versatility speed, your 12/12-9.3x74R drilling with a red dot is hard to beat many call it the poor man's double for cats.