Does anyone know how accurate a hand held GPS is for speed?

then you have my Garmen etrex legend that said I was going 200+ in my jet boat in a nostalgia race.

diff between a $99.oo gps and a $180.00 gps.  but when you turn it on it says how much error there is in distance, withing 15 ft etc. it would seem the lower the error distance is the more accurate speed would be, also (and i might be wrong on this) but don't some of the more $$$ units use more satellites for their readings, seems my old cheapo only used 3 sats and my new one is like 5.

Megellan claims there receivers have an accuracy in Velocity of 0.1 knots (RMS)
If you own a newer model with up to 14 channels (sattelites) like the cheap models, Explorist Series.
Have to check with other manufacturers for there accuracy numbers but I would think they be close to the same.

-Rebel