OCC has published a review on the Sapphire HD 7950 FleX Dual-X Edition 3GB video card

Overclocking this video card is as simple as booting up the Sapphire TriXX utility and moving some sliders around. I started at a baseline of 1050MHz on the core and 1500MHz on the memory. I took bigger steps on the core, making the jump from 1130MHz to 1150MHz and began to saw artifacting and snow start to show up. Backing down 5MHz at a time, I regained stability at 1135MHz, but I took it down another 4MHz to be conservative. The memory performed great and was rock stable until 1560MHz where it basically hit a wall. A few MHz here separated the memory from running great and complete failure. Compared to other HD 7950s, the clock speeds presented by this one aren't as impressive - although the idea to this card is multimonitor support and not raw overclocking potential right out of the gate.

  Sapphire HD 7950 FleX Dual-X Edition 3GB Review