Hm, well Wonder Room doesn't really accomplish much, especially since Gallade has much more balanced defensive stats, even if they aren't that strong to begin with. Gallade tends to perform better with Swords Dance and generally wants that coverage slot to deal with not getting walled. Bulk Up/Substitute/Drain Punch/filler could be an option though, not sure how well Mega Gallade pulls it off. Regardless of set though, 252 Att / 252 Speed is probably the best EV spread for it. The fact that it doesn't have a speed boosting nature is tough regardless though, since the base 110 speed tier is incredibly important these days.