I was curious about this because Both on has 100 base Attack and Speed. The only thing that worries me is Flygon's base 80 defenses. I would gladly welcome input! This is my current set:
[email protected] Life Orb
IV's-All best except for SpA
EV's- 252 Att 252 Spd 4 Spd
Dragon Dance is good but if you put a U-Turn in there when it's weak or you want to get away.
I think your set is good, flygon is fast, it will use dragon dance before a lot of Pokemons.