Just looked at my notes, I did a good size two bone CAB rib roast last X-mas. Started out with a cold smoker(sm020) at 180* and it took 5 1/2hrs to reach 128*. I did the reverse sear as dls talks about. My KISS rub was Montreal Steak seasoning and some Kosher salt.
Smokin' has some good Au Jus recipes in his Prime Rib 101 PDF.