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I don't think you'll save much time. I've cooked 4.5 pounders and it still took 9 hours to get to 195° on my UDS running in the 250s.
Shouldn't be a problem with dryness though. Safeway here usually only sells 4 or 5 pounders. I think they cut the big ones in have and sell them separately. I've done several and never had a problem with one being dry.
I cut one in half once for the purpose of more bark with a side effect of quicker cooking time. Took about 6 hours total plus rest time. It worked for quickness but it wasn't as fall apart as normal.