'TrevCoult' from Tamiyaclub pointed out something interesting the other day, particularly if you want to run a 'balls out' motor.
The Super Astute pinions, which go down to about 18 or 19T are the same 0.5 module type as the kit DI gears. They are still available on the 'Bay for £5 a pair. These:
http://www2.towerhobbies.com/cgi-bin...1&I=LXEX40&P=K
should also work.
Elliott.