we exclusively use GB 280x Rev 2. 740KH/s, easily undervolted, run cool, are almost silent at 80% fan, and are just flat awesome.
Did you bought it earlier like last year or very recently?
The fact is old Sapphire 280X were good too,but now they are worth lot of troubles.
I am trying to find out which cards currently(meaning even if they have been modified like Sapphire 280X) are best for mining.
Both. Just got more in last week, and even more coming in this week. The newer ones run at a higher stock voltage, which means a lower binned chip but hash just the same.