I thought I'd post up some numbers from my most recent cook, just to add to this thread for future reference.
Did two 8-9lb butts, injected and then with rub. Ran my WSM between 230 and 250 overnight (with large water pan). Took them off at 190 internal after just 12 hours (by far my fastest cook ever). Double-wrapped in foil, then each wrapped in an old bath towel, then both tucked into a smallish cooler. 8 hours later, removed one butt for a birthday dinner, and it was nice and hot. Really juicy, too. TEN AND ONE-HALF HOURS after I took them both off the smoker, I retrieved the second butt from the cooler and temped it with my Thermapen at 134-136. So the 'cooler method' nets not only some tasty shoulders, but a long-lasting kind of suspended animation of food safety.