Of your two choices, I don't think it matters. See Mule Deer's post. I've read John Kingsley-Heath's book and he's right. Those who use heavier rifles on leopard are usually hunters who hunt other game on the same safari and don't want to bring more than one rifle.
I don't believe in hunting dangerous game with a single-shot rifle, though with a leopard you'll probably only get one shot anyway.
