I run a 4600kV motor (don't know how many turns it is) with 79T spur and 23T pinion - the temperatures seem good in this config for both ESC and motor, though I think I could run it with a slightly bigger pinion. For the club track (clay with a reasonably short straight) it works very well imo. Here is a video of the track:
http://www.youtube.com/watch?v=YkBn5aEmnrc
For the longer tracks like Kampenhout and Arendonk (both Astroturf, Arendonk has a humongous straight) it lacks some top speed - I could solve that with the gearing, but I guess a quicker motor would be better (hence why I bought a 5200kV motor).
Kampenhout:
http://www.youtube.com/watch?v=XlgcmO1csp8
Arendonk:
http://www.youtube.com/watch?v=tbCrDOrbMuQ
What I'd recommend you to do in the long term though is to find a gear ratio that works for you with the kit spur and then get a smaller spur and pinion so the motor is further forward. It's visible in Lee Martin's (amongst others) setups for astroturf, and though my car felt good without it, I can imagine on dry astroturf it would help get the car to perform that little bit better
