Put Your Hand in the Hand of the Man from Krypton
But what the hey. I'll even go one better today, and use a scene from a Silver Age dream sequence. It doesn't even have to make sense on its own terms. Still, it caught my attention. It's from "Superman in the White House," originally published in Superman #122 in July 1958:
Now I'm not going to dispute Superman's capacity to shake a million hands; I don't doubt him there. (Though I'm a little curious where this "custom" of Jimmy's came from, and how all those people got on the lawn.) But what does it mean to shake a million hands?
If he was reasonably fast, and took exactly one second to shake each person's hand, a million handshakes would take exactly 11 days, 13 hours, 46 minutes, and 40 seconds. "Won't take long at super-speed"?
So how fast would Superman have to move to actually get the job done quickly? Let's say, three hours of nonstop superspeed hand-shaking. That'd do the trick if Superman spent 1/100 of a second on each person. Somehow, I doubt the experience would be memorable for any of those million. The effort hardly seems worth the result.
By the way, if you haven't already bought one of the first two Showcase Presents books, you're doing yourself a disservice. $10 for (in Superman's case) 29 issues of comics? It's very nearly a quarter box in TPB format.