Today we had a training day on our local track.
I've used 2 PDA's with 2 GPS units: 1 PDA is Win2003 IPAQ and the second one is Win Mob 6 PRO.
The GPS units I've used both 1HZ, one is Bluetooth and one is a mouse GPS.
The system worked PERFECT!!!!!
As we have not measuring system on the track (our country rules forbidden motor sports so we can not officially race...), that is the only solution.
So, now I'll be buying the 5HZ unit just to get a better results out of RC.