Accelgor with a benficial nature and 252 Evs in Speed has the base speed of 427. It's fast enough. Besides Me First is not viable. I have my funny reason:
My friends were battling one day (this was before I met them) in Pokemon B2W2 and one of them had a Me First Mewtwo, the other an Explosion Skuntank. If you put two and two together you know what happened. They sent me the replay and to this day I can still imagine the exploding Mewtwo.
It's better to give it a Life Orb. Now you have Speed and Power!
Hopefully I Helped!