Action Comics #314 (1964) - Superman becomes The Flash
While trying to collect all of the Superman/Flash races, I came across this gem. Superman actually becomes the Flash.
Well, the story is an alternate reality story. In it, we learn that Jor-El had 6 possible planets in which to send his son. On each one, the environment and Superman's powers would have been different. So, on each of the different worlds, Superman would have become an approximation of one of the other members of the Justice League. For instance, there was a water world in which he'd be like Aquaman. A world where he would have no powers but would become like Batman. And, obviously, a world in which he only gets his super-speed and becomes like The Flash. I'm surprised they didn't go with the Superman-Batman on the cover as the first popular Flash-Superman race wouldn't take place for another three years.
All in all, a fun and wacky story. Unfortunately, there was not a world in which Superman becomes a gender bending version of Wonder Woman.