I think that you'll wanna go for a Mega Diancie when ORAS comes out. The IVs and nature you have on your Diancie are more suited for it's mega evolution, where it gets increased offenses and speed but lower defenses.
So you'll want to go for max Speed EVs. As for Attack and Sp.Attack, it's probably best to either go full Sp.Attack or do some sort of mixed set.
Nah ンン
“No, I... I have to be strong. Everyone expects me to."