1G = 1200 kph
2g = 2120 kph
3g = 2850 kph
4g = 3400 kph
5g =3840 kph
6g = 4200 kph

Using this data, These are "Maximum" speeds for streamlined craft, 
figure cruising speed is 75% of these and 
Nap-of-Earth (NoE) speed is at max 25% 
(NoE speed is really dependant on the ship's electronics package, 
as such commercial ships will be slower than the computed speed 
as the pilots primary sensor is the MK 1 Eyeball)