When overclocking the Sapphire HD6870 we used Catalyst Control Centre.
Our overclocking tests were reasonably successful considering this is a reference cooler, although we didn’t find huge overhead on the core. We were limited to 950MHz on the core and 1,140MHz on the memory.
We then wanted to run some tests with our overclocked results, settling on 940MHz core and 1,140MHz memory for the final CrossFireX settings.
The overclock results are healthy, Unigine Heaven Benchmark shows a 2fps increase in and 3DMark Vantage scales with 300 additional points when overclocked.Sapphire Radeon HD6850 and HD6870 Review,