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As NOLA mentioned, go as low as possible to maximize the butt's exposure to the smoke. I usually get 2 1/2 hours of good heavy produced smoke, and by this time my internal is around 140 degrees. I continues unwrapped until the butt's internal reaches 160 degrees, then it get's wrapped in foil and returned to a hotter grill for the final portion of the cook. I go to 210 degrees, but mine butts are injected..