Depending on your temps now, I would try 18/68 first. Have you seen the outrunner-inrunner hybrid thing on hobbycity.com? Seem like those might be pretty friggin strong if they have the torque and power of an outrunner.
http://www.hobbycity.com/hobbycity/s...trunner_2900kv
http://www.hobbycity.com/hobbycity/s...trunner_2000kv