Bow wave could indeed be used to estimate speed in real life, and can also be used in SH, although as in real life, it would probably be one of a few observation sources which would be combined to get a figure.
German WW2 Type XB boats occasionally had false bows painted on their sides to make range and speed estimates more difficult for the Allies in a manner similar to a technique used on several combat aircraft these days (such as the F/A-18, which can often be seen with a false canopy painted on its underside to confuse enemies in a dogfight). There is an artist's impression of V-119, a Type XB U-Boat with the false bow scheme in the Squadron/Signal publications 'U-Boats in action' (ISBN 0-89747-054-0)
I sometimes use bow wave alone as an estimate of speed if I'm in a rush to take a shot of opportunity when I haven't got the time to do a stopwatch estimate, i.e. when a battleship is in my scope and I'll never be able to do an end-around on it.
You get used to guessing speeds this way if you do it often enough.

Chock