i would base my purchase on noise, since that is something important to me.
Techpowerup always takes a noise measurement:
Based on that criteria, I would pick this card:
Sapphire HD 7770 Vapor-X 1 GBhttp://www.techpowerup.com/reviews/Sapphire/HD_7770_Vapor-X/27.html
As far as the performance chart, techpowerup says it's equal to 6850.
If your rig is already a hairdryer, then there's no point though...