you need powered riser cables as well...
Why is that? The 270s have a 6-pin power connector, that is enough, isn't it?
then how you plan to attach them main board??
you also dont buy 270s
buy 2-3 280 will do same performance
With the risers, did you even check out the second link? I'd like to see some hash results from the 280 if you don't mind, I'll check it out.
The R9 280Xs are going for $385 here, and only get to max 800KH/s, 270s though are $220 and reach 450KH/s-480KH/s. Idk what to go for :S.