Thank you!

Indeed if you scroll down you will see that this topic has been thrashed around massively already here. But yes it's the internal temperature that matters. In a home oven you will hopefully end up with more or less medium-well done end pieces and rare in the middle.

Do you have a thermometer? That's really the best way to check for doneness. 130 degrees fahrenheit for medium rare. That said, if you have the time I would try this technique from Serious Eats: http://www.seriouseats.com/recipes/2009/12/perfect-prime-rib-beef-recipe.html. 3.5-4 hours at 200 degrees then rested and seared. Good luck!