Just wanted to thank Y_H and others in the forums for all the posted info. Completed my first cook yesterday (2x b-backs and a 3lb tri-tip). Ribs came out well and in almost exactly the 4 hour time frame expected (275, no wrapping). I probably slowed them by having the 640 open a couple times when adding the tri-tip late, Only oddity for me was the ribs plateaued at around 182 three hours in and never exceeded that temp per two different thermometers. At the four hour mark they did meet Herb's described fold/bone twist test so they came off before the tri tip sear.
All said I learned a lot just in terms of the process (some steps/phases were trickier than I'd thought), coordinating the two different meats' timing was good experience, and everything came out very well. I know my first failure still looms in the future so I'll take lucky over good any time!