Cook it at 250, then do the scratch test. Take your fingernail and test the bark, if it holds, then it is ready to foil, if the bark moves when you scratch it, then give it another 30 minutes and try again. Usually when the bark is ready, you are in the plateau stage 145-165 degrees, once there, wrap your pork butt in a double layer, sealed, wrap of foil with some water, beer, apple juice, etc etc, then pop that maverick thermometer in and pull it when it hits 200 degrees. Then let it rest for an hour. A 6.5 pound butt shouldnt take more than 9 hours or so if you foil. Good luck man