also i keep on seeing 2200mAh li-po's, why not throw on one of those instead of a 1200mAh? they look about the same size. was that a stupid question?
The only problem with running a bigger battery is the motor will get a lot hotter which will shorten the life of the motors, if you put heat sinks on the motors (main/tail) to help get rid of the heat you should be fine. I run a 2100mah on my little Hummingbird with heat sinks on the motors and I've never had a problem.