I've cooked 2 or 3 standing rib roasts for Christmas dinner for well over 10 years now. I typically buy 2-3 roasts from the small end about 6-9 pounds each--depending on how many we are feeding (usually 10 or more). I ask in advance who like med rare, medium, or med-well. I over buy because we all like left overs. I buy the roasts 3-4 days before Christmas and dry age them in my beverage fridge in the bottom drawer on a backing rack over a bed of rock salt at 33-36 degrees. I but a couple of my wine fridge thermometers in thbe fridge to make sure I hold that low temperature without freezing the meat.
The afternoon before cooking, I turn the temp up to about 45 to start warming the meat toward room temperature. I get up early and take the meat out to continue warming it to room temp.
I rub the meat with olive oil and season it with fresh ground black pepper, rock salt, a little crushed garlic, a sprig of rosemary and thyme, and a couple sage leaves and place them on a rack in a large uncovered shallow roasting pan.
I insert electric meat thermometers in each roast and start roasting them at 200 degrees and plan for approximately 50 minutes per pound to get medium rare.
I target 123 degrees for med rare, 138 degrees for medium and 150 for medium well (too well). The roasts go in at about 7:30 AM for a 6 PM dinner. I plot the temperatures ever hour to see if I'm on track based upon a spread sheet from the last 5 years. Note that the temp raises much faster per hour in the early hours and then much slower in the later hours.changes ( a function of thermal dynamics and the delta between the meat and oven temperature)
Anyway, don't panic if it appears to go up too fast. As each roast reaches it's goal temp, I take them out a rap them with two layers of heavy duty aluminum foil to rest. Note that the core temp will continue to rise 5-8 degrees, and then start very slowly dropping (not to worry if dinner is still 2 hours away).
After all the roasts are done and rested at least 30 minutes and about and hour from dinner, all go back into my oven at 500 degrees for about 15 minutes or until my kitchen smoke alarm gos off. By then they are all ver dark brown on the outside, but uniformly perfect throughout the center.
I rap them back in their aluminum foil to rest until sliced for dinner. My wife makes a great gravy at this point in the roasting pan by deglazing it with red wine and beef broth.
Hope this works for you.