It doesn't take much to kill humans with one punch. Some really strong men in real life can do it, and have done it. Has he showed anything else other than one punch kill humans? Goku back in Dragonball series already showed he could knock people out by the air pressure alone (without physically touching them).Vash, you're not necessarily right. It hasn't been quite established how strong Saitama is yet. For all we know, he might simply be omnipotent. I think we cannot answer this question until OPM is completed - It would be unfair, as Goku had many more chapters/enemies to become stronger. Personally, I have a hunch that Saitama is actually stronger.