I have cooked 9.5 lb pork butts several times, and they usually take about 24-26 hours in my smokette when set to 225. I did one last weekend and decided to see if I could do it in less time - put it in at 6:30 AM at 225 - turned it up to 250 at around 5 and pulled it out at 7:30 - temp was only 185 but it pulled pretty good and tasted great.
I agree with those that say "It's done when it's done." I may try a higher temp next time, but knowing what works for your equipment is what's important.
I have several recipe books that say you can grill a whole spatchcocked chicken at high temperature for only 15 minutes per side. On my grill I've never been able to do one that quick that wasn't burnt on the outside and raw on the inside.
Recipes and forums are great sources of information, but in the end you've got to do what works for you, then write it down or remember it so you can repeat it.