Actually since how EVs work, being just additional 63 stats at level 100 and natures, you’d be much better off investing your EVs into Speed and HP.
A 252 Atk / 252 SpA Quiet Hoopa Unbound has 419 Atk and 482 SpA, with a combined 901 offense. Meanwhile an uninvested Hoopa Unbound has 356 Atk and...