There's an old issue of The Amazing Spider-Man (in the 280's I think - 282 maybe?) where Spidey fights Manslaughter - a boxer with no pain receptors. He's chasing Spidey around a room trying to smash him and doing a fine job of wrecking walls and furniture. Then Spidey gets fed up and stops one of Manslaughter's punches with his open hand. Manslaughter was still just a normal human with normal human muscles - Spidey's little hand stop created enough concussive force to knock Manslaughter out cold. It was a great display of Spidey's proportionate strength of a spider and helped solidify to me how powerful Spider-Man really was. It was also a great issue overall, as it had Spidey reunite with Crusher Hogan, the wrestler he beats in his first appearance as Spider-Man.