I use the stock tank in mine and easily get 12 mins out of it. Remember, Your going to be at 1/3 throttle or less most of the time.
I had the ball link for my throttle fall of one day right after takeoff. The throttle was stuck at about 3/4 and it flew for about 7 mins till the tank was dry. So, with a little throttle management you wont even know you have only a 6oz tank in there.