ok thanks for the tip bro. I also have another doubt, I don't know if I should get:

1) 2 x R9 270 + 1 x sapphire R9 290
or
2) 2 x R9 270 + 2 x 7870 sapphire ghz edition

What do you think? I thought of the 2 x 7870s because I live in a very hot area, and from what I've read the reference 290 cooling is not that great. Also I can get them slightly cheaper than the price of 1 R9 290.
The kh/s should be similar at around 800-850 right?