I'm not saying the OP did it wrong, but I cooked a nearly identical sized prime rib for Christmas. I put it in the oven, on convection roast for *10* minutes at 550. Sorry, Magnus, I would have seared it in a pan on the stove, but didn't have a pan large enough. After 10 minutes were up, I dropped the oven down to 225 degrees. And I certainly didn't have it in there for 3.5 more hours. My guests were thrilled that it was nice and pink all the way through. Except for two guests who like it well done. For them, while the roast was resting (and the broccoli steaming, and the
twice baked potatoes with bacon & cheddar cheese baking for the second time, and the corn cooking - I cranked the larger oven to 500 & started heating up some cast iron frying pans. And... they were thrilled as well. And, what's good about my stove is that I have two ovens, so I can bake the potatoes at one temp while cooking the roast at another temp.
