Personally I would go with the Sapphire card. I have never seen one die, lol. I once had 2 x HD3870's and a HD5870 from sapphire as well. All 3 cards are still going good today in friends systems that bought them from me on the cheap. lol.
This time around I went with a MSI Twin Frozer HD7950, and it's been great so far. Well one of the fans was making noise for a bit, but it went away on it's own. Must of been dirt in the fan that was causing it. lol.
I have a buddy that had a Powercolor HD6950 that bricked within a year. He sent it in for a replacement and the replacement died within 3 months. So I tend to recommend against Powercolor based on his experiance. After that fiasco, he decided to grab an XFX HD7950 and is now going though the same issues. So now I have XFX on my not to buy list as well. lol.
I know this is probably not typical for everyone that buys Powercolor/XFX, but after helping him with all the headaches I will stay with what has never failed me yet. Sapphire/MSI. Asus and Gigabyte are good as well from what I've read from customers, but I have never had one of their cards so I can't really say anything about them based on mine, or any of my friends experiances.
As for performance. What ever card has higher stock clocks would be faster obviously. If you overclock they should/will get to about the same clocks either way, unless one of the cards is voltage locked. Not all cards will clock the same either. It's hit or miss with each individual graphics chip in the same way that CPU overclocks works out. My HD 7950 with voltage increased can clock my core to 1150mhz(880mhz default), and my ram to 1500mhz(1250mhz default). Not bad, but I have seen Twin Frozer HD 7950's hit 1250-1300 core stable as well. So it's luck of the draw really...