You definitely want to change the motor. 12:1 gears don't have much torque. 22TPA motor and M120 is what I use on a build like that. Short stroke does not increase trigger response, not noticeably anyway. It lowers the FPS by around 15FPS per tooth removed, approximately. You want to use a heavier spring like a M120 when using 12:1 gears to prevent PME, but that will raise your FPS, so you short stroke your gears to bring back down the FPS.