Taken from some game forum:
As a matter of fact, the doomguy runs faster than 30mph.
64 units = ~2 meters.
Player speed, running = ~570 units/second. (This comes from a test I made and might not be precise, you could get an exact value from the source code).
Meters per second = 570 / 64 * 2 = ~18.
18 meters per second = 65kph.
And this doesn't include straferunning. With straferunning, the doomguy runs at speeds around 90kph.
I don't think this guy ever played Doom. Maximum 100% health? I guess he wasn't good enough to get any orbs. Also, this footage is not from the SNES. The SNES was not fast enough to render all the textures, so the floor and ceilings did not have any.