New GPS system.

[HBRC]

i have the Garmin 305 on my bike. I've thought about putting it on my RC car too.
The speed is actually registered quite quickly, and adjusts quickly.
It won't be perfect, but good for reference.

And you could check the height of jumps with the altimeter...

oh, and the best price I've seen on the 305 (same as 205 but without the HeartRate monitor i think) is $325.