I'd take a .450/.400, but they were very regularly hunted with lighter rifles. King George V used a double .280 Lancaster. The .303 was widely used.

I evaluated a .400/.360 Westley Richards NE hammer double a while back that had a gold inscription from one Maharaja to another on the rib. They guy that was thinking of buying it had a book written by a Maharaja about Indian hunting, and who had done a lot of tiger hunting. He favored a .400/.360 WR NE hammer double for tiger, and was pictured with it in the book. Sure enough, it was the same rifle. It would sure work on tiger, but I would want a bit more punch.