Dude, johnyguru blasted that psu, said it was a pos....but in a nice way. Now dont take it personal, hell i just upgraded from that exact psu a few weeks ago. The thing was starting to just shut the pc off with no warning....which is a warning in itself if you think about it. It didnt even make its 80+rating also power ripples and ... the list goes on. In forums i would say the name of my psu and the card i was to oc with (matrix platinum) and people would laugh and were surpised id not blown all my parts up yet with that psu.
Here is the link for johnyguru and his review of the GX750w psu.
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story5&reid=188 read for youself if you want.
Now after reading that would you trust BOTH your expensive GTX580s to it. If your not going to oc the cards a quality 750w is fine. The ROG Matrix Platinum when overclocked and overvolted will eat 650w (whole system), you want to put to cards on that powersuppy.
Now with that said, if i had to id do it.