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.