Depends,

This can get a little technical. In a kill situation, one wants to create the largest wound channel with the greatest penetration. A garret .458 520 grain hammerhead bullet with a huge metplat will create a lager wound channel than a .500 520 grain round nose. It has to do with the leading edge shock wave that flat "point" generates passing through flesh. However, in a stopping situation a .500 probably will be more effective shearly due to greater ME. I've read that the best lion stopper is a 458 lott. Why? Because the shock that a 500 grain bullet imparts on the nervous system above 2500 fps is devistating.