The kv rating of the HV 6.5 motor is less than most of the smaller 540-size brushless motors. If you run it on 2S it will probably be tamer than you think. The only issue is running the HV motor on only 2S won't get the RPMs up into that 30k range where you'd want to be. I don't think you have to worry about damaging your drivetrain, but it might not be the best setup you could run either. Give it a try and see how it performs.