Yeah man so there's really no need to run Agility on it because it's in the top speed tier after it mega evolves. The most successful set looks like this:
Metagross @ Metagrossite
Ability: Clear Body
Level: 50
EVs: X HP / +X Atk / X Def / X SpD / 252 Spe
Jolly Nature
– Iron Head/Hammer Arm
– Zen Headbutt
– Protect
– Substitute
Zach Droegkamp, Major Bowman, Aaron Zheng, and Alex Ogloza have all run variations of this set. The X's signify investment based on specific hits, with the rest dumped into Attack (+X).