I had a Saphire hd4850 x2 and it ran without problems.
Now I own a HIS 4870 1GB and it runs great too, when I buy my second card, I'll check both companies pricing and then decide, but I would prefer to stick with a same brand so hopefully HIS will drop the price down.
not really worth paying the extra $95 for same card.
What I did I got the HIS hd4870 1gb for $189 last week and I ordered the Acellero Twin Turbo after market cooling so total price of $223 but my card will be clocked at 830 - 850 MHZ and will be super quiet, what I was going for in the first place...
Even without the after market cooling the card is relatively quiet and it over clocks to 790 MHz.
So in other words, get the best priced card. Except ifor the cooling they dont really differ that much in the design.