So the plain will go the same speed as the CO.
not necessarily. Generally they test how far these cards will go. If it can't hit the CO speeds, they knock it down and call it a vanilla. They do the same thing with CPUs. However, if there is a huge demand for the vanilla cards, they'll take a card that's perfectly capable of CO speeds maybe even higher, clock it down and call it a vanilla, in which case, THEN you'd be able to get the higher clock speed.
Regardless though, evga has a good warrenty, sooooo even if you trash the card, you can get it replaced although that's not a very good way to go about it
The CO one could be using slightly better components and hit like 600/1600 for all you know, whereas the vanilla may max out at CO speeds, IF that. Ya never know, overclocking isn't an exact science. For all I know that vanilla could do 900/2000 on air! (not really), but you get what I'm saying