While this may be true when the 7870 released its not the case anymore. The new drivers fixed most of the problems it had on release as well as improving performance. Idk about the sapphire cards though. Imo the 7870 and 660ti are both great cards you can't go wrong with either one.
I can speak from experience with XFX they have amazing customer support that lifetime warranty is amazing. I had no trouble getting them to honor it.
Does anyone know if i can activate these games on steam i was looking into getting a 7870 to replace my 6850?