On the one hand, treat them as you would the total 10 lb weight & use a meat thermometer. Because they are smaller than a single 10-lb roast they probably will finish sooner than one large roast. See method & recommended temps in Serious Eats, here:
http://www.seriouseats.com/2014/12/food-lab-guide-to-prime-rib.html
On the other hand, you have two pieces of meat. Is the oven big enough to roast them with enough air around each to make sure the heat circulates and penetrates? Cook in 2 roasters, or one large one where you can maintain the space between the pieces of meat.
Also, most ovens have uneven heating or hotter and cooler spots, so for prudence, I would have them bow to their partners, and change corners or sides two or three times during the roasting.
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http://www.seriouseats.com/2014/12/food-lab-guide-to-prime-rib.html
On the other hand, you have two pieces of meat. Is the oven big enough to roast them with enough air around each to make sure the heat circulates and penetrates? Cook in 2 roasters, or one large one where you can maintain the space between the pieces of meat.
Also, most ovens have uneven heating or hotter and cooler spots, so for prudence, I would have them bow to their partners, and change corners or sides two or three times during the roasting.