While it's true that .375 H&H is frequently the legally stipulated minimum for lion, I've yet to meet a PH who felt that made a lot of sense. Cats of all sizes are made the same way -- they're designed to dish out damage, but they're not really made to take it. Moreover, their highly attuned nervous system does seem to make them more susceptible to system shock than many similar sized animals. At least, that's been a notable observation in my own experience having shot lynx, cougar, caracal, leopard, lioness and lion.
Not for a moment am I suggesting that a 450 lb lion isn't something to take extremely seriously -- in fact, there aren't many critters you should be taking more seriously. But there are a whole lot of PH's out there who feel that something along the lines of a .300 Magnum shooting a 180 grain premium softpoint is all that's really needed -- and that it's possibly even better than a .375 with its lower velocity and more heavily constructed (and often slower expanding) bullets. Of course, YMMV, and it's never a bad plan to stick with whatever the regs say in the region you're hunting.