I cooked eight 2 1/2 pound butts saturday (they were a steal, i usually buy ?em 6 to 8 pounds).
They took 10 hours at 240- 270, but even though they had very little visible fat outside, the meat was very good and moist.
Pulled easy and had to dumb nothing, really no waste at all...Plus you get more bark when doing smaller butts.
I think the temperature is the most important thing for butts, because i?ve had more fatty butts of 4-5 punds done in 10 hours too.
Don Marco