As a professional chef I prefer to cook my PR to 110 degrees and allow carry over to work for me as it rests. As you pointed out there are differing ideas of what is rare.
Prime rib is usually served MR and the lower temp keeps the rare and MR fans happy. (personally I like mine rare as possible)
When we serve if a guest wants a medium cut (end cuts often go fast) we simply pour hot jus over the top of the slice. Most are very happy. If the guest wants med well to well done we resort to the aujus in a pan and put it in the oven method.
Choice is what most restaurants serve.
Most people will be very happy with Choice and will complain that your Prime cut is too fatty.
Here is a link that shows the difference between Prime and Choice. http://simplyrecipes.com/recipes/prime_rib/
I use a simple rub of kosher salt, fresh cracked pepper and fresh garlic. Sometimes fresh rosemary of thyme.
I just got an FEC 100 and seasoned it up this afternoon. Tommorrow night a load of butts is going in and am looking forward to serving up some smoked PR on Friday nights.