I've seen that recipe before and heard from others that it works well. I would stay patient and not open the oven till the end when I would check internal temperature with a thermometer to make sure it's cooked to your liking. The high temperature start should sear in the juices nicely and then it will slowly cook inside. Let us know how it comes out.
We're having a prime rib for Christmas dinner too but we've come to love using our Ronco "set it and forget it" rotisserie. I love using it for roasts, chickens and even a small turkey.