OCC has published a review on the PowerColor Radeon HD 6870 PCS+ Call Of Duty Edition

This card is factory overclocked with clock speeds of 940MHz on the Barts core and 1100MHz on the GDDR5 memory so you get a boost in performance to start with. When it comes to overclocking higher, there is some headroom left on the HD 6870 PCS+, though not much. On the core overclocking I was able to push the card to a clock speed of 1003MHz (63MHz) and 1208MHz (108MHz) on the memory. This amounts to increases on the order of 6.5% on the core and just under 10% on the memory. These increases, although slim, still offer measurable gains in performance across the test suite.

  PowerColor Radeon HD 6870 PCS+ Call Of Duty Edition Review