Go with hammer arm. Alot of pokemon have alot more than that. If you lower their speed, you will probably not outrun them. If you have gyro ball, hammer arm is perfect. Emboar is usually not very fast (a maximum of 251 which isnt much) & he is used as a slow sweeper because of his high attack/ Sp attack, or a wall when you teach him curse. I would go with hammer arm because it can 3HKO them in the worst of cases unless it is a flying, psychic or both.
Hope this helps: .