I use a very similar Dialga set. Instead, mine is just standard max health (248 probably better I know), max sp def and 4 in sp.atk. Instead of Rest though, I use Iron Head, allowing Dialga to become a Xerneas check, while having a STAB move at the same time. It does require a sassy nature, but you do get added suprise value instead. Definitely Roar over Toxic.
Rest Dialga is probably better on stall teams, while mine is more fit for balanced (or offensive that needed a Steel type, Stealth Rock user, Roar and something to take on Xerneas all at the same time, in the case of the team I created it on XD)
Rest Dialga is probably better on stall teams, while mine is more fit for balanced (or offensive that needed a Steel type, Stealth Rock user, Roar and something to take on Xerneas all at the same time, in the case of the team I created it on XD)