Course it is - what is subject to discussion is the best way to get the most out of your legs
Did this out of interest for someone my size on a flat windless road - sounds about right (roundings though):
100 w - 26.4 km/h
120 w - 28.3 km/h = + 1.9
140 w - 30.0 km/h = + 1.7
160 w - 31.5 km/h = + 1.5
180 w - 32.9 km/h = + 1.4
200 w - 34.2 km/h = + 1.3
220 w - 35.4 km/h = + 1.2
240 w - 36.5 km/h = + 1.1
260 w - 37.6 km/h = + 1.1
280 w - 38.6 km/h = + 1.0
300 w - 39.6 km/h = + 1.0
320 w - 40.5 km/h = + 0.9
340 w - 41.4 km/h = + 0.9
360 w - 42.2 km/h = + 0.8
380 w - 43.1 km/h = + 0.9
400 w - 43.8 km/h = + 0.7
420 w - 44.6 km/h = + 0.8
440 w - 45.4 km/h = + 0.8
460 w - 46.1 km/h = + 0.7
480 w - 46.8 km/h = + 0.7
500 w - 47.4 km/h = + 0.6
520 w - 48.1 km/h = + 0.7
540 w - 48.7 km/h = + 0.6
560 w - 49.4 km/h = + 0.7
580 w - 50.0 km/h = + 0.6
600 w - 50.6 km/h = + 0.6
http://www.kreuzotter.de/english/espeed.htm