So.. your dilemma is should you pick 7870 of company A or company B?
Thats the simplest problem you can have- pick the cheaper one, or the one with longer warranty. If they're both the same, pick OC version.
OC version is unlikely to be more than 5% faster, witch translates into- you're not going to notice it being faster in games, but the price or warranty- you might.
i think that's it. it's between A or B product. because i don't know much about Graphics Cards. so they're not the same which is Sapphire is Ghz Edition OC while PowerColor is only Ghz Edition. so i better go to Sapphire even though PowerColor is a lil bit more high on core clock.