Using the Catalyst Control Panel we were able to overclock the Radeon HD 7870 from a 1000MHz core and 1200MHz memory frequency to 1220MHz and 1275MHz, respectively.
The Radeon HD 7850 on the other hand didnt overclock quite as well. The core went from 860MHz to 975MHz, and the memory faced the same limitation as the HD 7870. Even with a 13% core overclock we expect to see a reasonable gain from the HD 7850.
On average our overclocked Radeon HD 7870 delivered 10% more performance, which in some cases was enough to make it faster than the Radeon HD 7950.
The Radeon HD 7850 saw an average of 8% more performance, which in some cases was enough to match the performance of the GeForce GTX 580.