There are many "beef roasts" Rib eye, eye of round, steamship etc.
A tough cut will get tender with slow cooking while a tender cut will turn to "butter".
Fat cap helps but is the roast marbled as well? Could be a small boneless rib roast or an eye of round.
One indicator would be how much it cost per pound. Rib should cost more that an eye of round.
I'd err on the slow side. Slow is easier to pull from the heat and retains more of its' moisture.
Any beef rub will do. Just don't over salt. Long cooking times tend to concentrate the saltiness. You can always add salt after. You can never take salt away.