Have to question some of the logic going on here guys. 3mph currents, consistant readings from water pickup speedometers meaning accurate ? Not sure where I have last run an RC boat with 5mph currents

GPS is very accurate for speed reading among other functions. A GPS can be easly moved from boat to boat.

Checking boat speeds with a radar may be accurate also but for true readings you need to be running toward the radar unit at full throttle in reasonably close range (not a good feeling when your holding the gun!!). GPS will record your top speed no matter where on the lake you are.

Radar guns (for something decent) are near $1000 where a decent GPS will set you back less than $100. Say what you like about water speedos and Radar but I think GPS is clearly a smart choice. (Might be why most who care about accuracy use it )