You may want to try the 1920/7 brushless motors made by Lehner. It is a highend motor and can run super efficient and super fast on 8.4 or 9.6 volts. You can use it as either a motor of torque or a motor of speed according to the configuration of the motor's wiring. Mike can get them for you if want them, but the problem with these things is the price. The 1920 series would cost you atleast 190 dollars in the best case senario. In size it is very similar to the 6s, but a little shorter. You can visit
www.lehner-motoren.de for more info and pics of this varacious beast.