Sapphire HD 7870 FleX Dual-X 2GB Review @ OCC
 

The memory clock was bumped up 25MHz at a time until things became unstable, then backed off 5MHz at a time till it would pass 30 minutes of Unigine Heaven 3.0. The core clocks were raised similarly. After a few rounds of testing the rock-solid clock rates were 1240MHz core (a 24% increase) and 1290MHz memory (a 7.5% increase). The core clock is one of the highest seen here at OCC and the memory is roughly what is expected considering the modules themselves were only rated for 1250MHz.

http://www.overclockersclub.com/revi...ire_7870_flex/