I have been cooking briskets (6 lb) at 250* full dry rub both sides of brisket.. 1hr smoke time.. 2 hrs cook time exposed.. then 3.5 hours wraped in foil until internal temp is 180*. I think you waste alot of time and money going any longer at lower temps. Yes you can cook 200 - 225 for 10 hrs... But why. It does not come out any better or tender... It has almost become this thing who can cook meat the longest....Try this method at least once before you comment 250* 6.5 hrs and you are done. I have tried to cook brisket at 220* for 10hrs I just dont get it.