To overclock both cards today we used Catalyst Control Center initially, then pushed higher with the Sapphire TRIXX overclocking tool. All of our samples overclocked to almost identical levels so the screenshots may not be directly linked to the cards in this review. This is because they are all the same reference design from the same production line batch.
First, the XFX HD6950 graphics card:
Our maximum overclock was only 50mhz on the core to 850mhz and a whopping 200mhz on the memory to 1450mhz (5800mhz effective). While the core has only limited overclocking headroom, the memory makes up for this. The quality of this Hynix memory is as good as we have seen.
Next, the XFX HD6970 graphics card:
The XFX HD6970 faired a little better on the core, peaking at 950mhz. Memory reached similar speeds to the HD6950 card, achieving 1475mhz (5900mhz effective).
If ever you needed to see the performance differences between the last generation and the current generation AMD graphics cards then this is a good test to run. Tessellation performance due to the architectural changes noted earlier shows that a single overclocked HD6970 is capable of performing close to the HD5870's in a Crossfire configuration! An extra 4 fps are also gained from the HD6950 in an overclocked states.
At these overclocks, temperatures on both cards rose by around another 3-4 C under load.