I just bred a perfect relaxed one of these with 0 speed IV

What do I do about the EV spread? I see 48 Def/252 HP/the rest SpDef all over the net but I dont see the reasoning

Moveset is

gyroball
twave
powerwhip
stealth rock

I dont know whether I should replace twave with curse though. Battlespot is too quick that curse might not mean anything.