Of course, if light, fast bullets are better than light slow bullets, than wouldn't it be best to have heavy, fast bullets? i.e. 45 ACP 230 gr +P rounds? Or the 10mm Auto?
It's all a trade game - you go big, heavy, & fast you're going to have more recoil and less controlability as well as less capacity in the magazine/cylinder. I think that with modern design hollow points, any round from 9mm on up will get the job done with proper shot placement - hopefully
because in the end analysis, a pistol round is a poor defensive weapon no matter how you look at it compared to a rifle round or shotgun.