I only use Royal Oak for charcoal. However that is mixed in with chuncks of apple, hickory, cherry or oak.
One major thing I noticed about the prime rib cut was it is not like a brisket, I pour LOTS of smoke to the brisket, however rib raost seem to asborb smoke quickly and be carefull try your first one with light smoke and let let the cooker breethe , exhaust stacks wide open, get your cooker real hot before putting in the roast. You know your cooker better than anyone though, so use your experience.
Sometimes the horseraddish bark might be a little bitter, but you are making prime rib and not a brisket..I have never tried adding Turbinado or sugar to the outside...Your favorite steak seasononing recipe added to the minors and horseradish is just plain ass awesome... Please post your ideas as I am always looking to improve.
Getting back to the smoke, the last rib I did last week I used hickory chunks only and my wife said it was on the edge of too much smoke, so experiment lightly to start...let me know!
When it's done it's done, so go have a beer..
Backwoods Fat Boy, TwinTech Pro Double