I used to work at a steakhouse. This is important:
There will inevitably be a woman at the table who can't stand the sight of properly prepared meat. Whether that woman is your wife or not, your wife will insist you cook the shit out of that roast. RESIST COOKING TO INTERNAL TEMP ABOVE 125. Instead, make a pan of hot au jus on the stove top. If any of your diners want their meat above med rare, throw their cut in that pan of au jus for 30 to 90 seconds. It'll cook up nice and quick without drying out or getting too chewy.
I'll Second this also: Worked in family restaurant for years, and we would have prime rib special every friday night, just get the meat to RARE, have a pot of Au Jus on the stove, when said diner wants a medium to medium well meat, just throw it in the Au Jus till it gets to the desire range, then on the plate it goes. Simple