OH YEAH! I forgot about that

. Yeah, I have that too. If only they gave you more time before the pokemon loses the PokeRUS.
It won't lose it if it's in a PC box. So have a couple carriers and spread it around and keep the carriers in the box for later usage.
I want to give it 252 in Sp.Atk and Speed, but I can never get pokemon to reach their full potential. I look to serebii for stats by the way. What would you suggest I do to yield the best results? It has a Rash nature, so at least that's right.
Well in Pokemon Black or White, for speed have it fight Basculin while surfing on route 1. 100% encounter rate, just avoid bubbles so you don't hit a Milotic which doesn't give speed. Feebas however does speed if you get one of those from a bubble. With a power anklet and the pokerus that's 12 speed EVs per fight. ((2+4)*2)
For special attack in black and white go to Celestial Tower. Litwicks and Elgyem both give special attack EVs. Should be 10 per fight with Power Lens and Pokerus. ((1+4)*2)).
Edit: Its IVs are probably not maxed and that would take months of ridiculous breeding (or cheating) so it won't hit its highest possible stats most likely. I don't even breed for IVs. Most people with perfect IVs used action replay or some other cheating device and that ruins the fun for me. You'll still get close. EV training's the big thing.