I've been looking through my setup sheets, and with a Thunder Power 8.5, I would run a 25/76 when used, so thats quite a move away from where you are at.
Your gearing needs may vary considering track, and motor specifics.
You can see gear charts on page 42 of your manual. If you dont have a manual, you can see a pdf of it here:
http://www.racing-cars.com/images/Te...sv2_manual.pdf