that's a great method if you have the time and a group that likes the same temperature (rare, med-rare, med., ect.). I rarelly have such a group that I serve, so I usually roast at 325 for about 20 min per pound with a probe thermometer at the center of the roast (measuring for my goal of medium-rare). Those who want well or med-well can have the end cuts while those of us who know how it should be consumed can have it med-rare still.
unless it's been dry-aged for a week or two, I haven't noticed much of a difference (for roasts) between choice and prime grades...then again...I haven't had too much experience comparing the two side-by-side...
prime grade is difficult to find and pretty darned expensive.