This will be interesting if this is for real but sounds like can only be bought as part of a system, but suppose it shows the cards potential esp GDDR5 clocks
http://www.techpowerup.com/64301/Diamond_Releases_Radeon_HD_4870_XOC_Unlocked_Black_Edition.html
http://www.techpowerup.com/64301/Diamond_Releases_Radeon_HD_4870_XOC_Unlocked_Black_Edition.html
Just reading now, but wonder if the memory timings slackened for that?
It's actually running 800/4400 (1100Mhz X4).