[Patrick]

The most gearing I've had on mine was 46/17 or 11.63:1, but that was speed runs on 6s, so it had more power to push the gearing. I'd say it would be a bit sluggish on 4s for racing.
For racing on 5s I've geared it between 14.1:1 and 16.5:1. It had a lot of power with 14.1:1, but my fastest times are with 16.5:1 (calculator estimates ~33mph) so top end isn't that important to me anymore.
If I get to try 4s tonight it will be geared at around 13.2:1.
Actually I did try 12.5:1 on 12 and 14 cells nimh once in my maxx around 8 months ago. 12 cells was a bit slow, but 14 cells seemed ok if you don't need the most powerful car on the track.