Yeah thats what i tought too. The performance upgrade isn't considerable. I think I'd get crossfire to work good, i have a Corsair 750TX psu, which is quite enough, and a Gigabyte 790fxt-ud5p mobo, so both cards would run in 16x mode, which is quite nice considering most mobos other than i7 ones don't have this..
The problem is I may not be able to buy a hd5850, they're kinda out of stock, I'm having a hard time finding one, but i should be able to get one eventually.
Thanks for the answer!