For those who have been wondering whether the original Flash, Jay Garrick, could exceed the speed of sound back in the Golden Age of comics…
Yes he could.
The speed of sound is roughly 340 meters per second (varying with humidity, altitude, etc.)
Earth revolves around the sun at roughly 30 kilometers per second.
So in that panel he was running at least 88 times as fast as the Flash: Rebirth promo claims was his top speed before he met Barry Allen.
Source: Flash Comics Miniature Edition (promo book taped to boxes of Wheaties in 1946), in which the Flash goes up against the one-off “Criminal From Tomorrow!” Dmane. And yes, that looks like the same stunt Superman pulled in the 1978 movie with Christopher Reeve.
I seem to remember that Jay reached the same levels of insanely impractical speeds that Barry did on a regular basis — this was just the first place I thought to look, since I remembered the time travel element.