Like already stated, a 650 would work perfectly fine. Lately the Corsair TX series 650 have been on sale for 70-80$ with and without mail in rebates. I just recently purchased a tx650w with the intention of crossfiring 6850's. My 650 was 51$ which was superb deal.
You could always go with Seasonic or Antec as well, whereas they are all great brands.It is really personal preference and what kind of deal you can get.
That Guru article really tells all and you will even have enough power to OC the cards and CPU, with a quality 650, if you would like.