I would say roughly about 15 min or so. Bear in mind that with that 11.1v battery, that motor is going to get quite hot if you fly around for 20 min. I would recommend keeping it to about 7 min flights or so, with time inbetween for the motor to cool down.

It should be a rocketship on vertical...

Im running a 11.1v on a GWS 350 in mine, and it has unlimited vertical.