For medium rare the Roasting thermometers always say about 145 F. I find it better to pull the beef out of the oven at about 140 and then let it rest in a warm place for about fifteen minutes, by which time the retained heat has made it perfect.
to get your roast beef just right to have it juicy and not rubbery tasting. you need to not only make sure that you cook it at the right temperature but also correct internal temp which is 145 degrees F. Slow cooking makes it juicy too for your enjoyment! hope this helps