I fly my speed 300 powered SS (6.6:1 gearing, 11x8 prop) with a 7 cell pack of 2/3A Nimh's. Around 18 minutes of cruise time on that pack.
Whare do you mount the battery. I tried my 7 cell 2/3a pack from my rc18t and could not get the plane to balance. The battery would have to be cenered between the front landing gear to balance. I finley gave up and bought a 1500mah 2 cell and it balances perfect with the battery between the motor and landing gear.