AMD Radeon HD 6870 Roundup
Author: James Prior
Editor: Charles Oliver
Date: February 13th, 2012
Overclocking & Temps
The performance testing shows that a small overclock has a small effect on game performance, so if you can get more performance for free by overclocking, it'll need to be significant to show worthwhile gains.
To overclock our cards we used variously Sapphire TRIXX or MSI Afterburner or, in the case of ASUS, Smart Doctor. Our final core overclock was achieved at the point where the 'voltage wall' is encountered - significant increases in core voltage only net small increases in stable core clock speeds. Stability testing as performed using MSI Kombustor at 1920x1080 with 4xMSAA using the sphere model. Once the core was verified stable under long term stress test, the memory clock maximum was found.
| Sapphire 6870 D3 | PowerColor PCS+ 6870 | ASUS 6870 dCU | HIS 6870 IceQ | HIS 6870 IceQ XTX | |
| Engine Overclock | 1025MHz | 1025MHz | 1001MHz | 990MHz | 975MHz |
| Voltage | 1.23v | 1.37v | 1.23v | 1.23v | 1.23v |
| Change | +11.4% / +105Mhz | +9% / +85MHz | +9.3% / +86MHz | +10% / +90MHz% | |
| Memory Overclock | 1250MHz | 1220MHz | 1212MHz | 1225MHz | 1200MHz |
| Change | +19% / +200MHz | +11% / +120MHz | +15.4% / +162MHz | +16.6% / +175MHz | +14% / +150MHz |
Evidently the HIS HD 6870 IceQ X Turbo X wasn't completely compatible with Sapphire TRIXX or MSI Afterburner, as any changes in core clock resulted in hard lock when stress testing. This appeared to be because the core voltage wasn't correctly set and defaulted to 1.175v, which is lower than the stock voltage of the card which ships with 1.23v to attain it's 975MHz core clock out of the box.
With our new overclock we decided to rerun the 3DMark11 Performance and Extreme tests, to see how the new clock speeds affected the scores:
The overclocks have neatly evened out the playing field, as around the 1GHz mark is where the easy overclock ends - showing how close to the edge HIS has taken their IceQ XTX. Next we measured GPU core temperatures at idle and under Kombustor load (30mins each).
The HIS IceQ shows how it's done for cooling, being the quietest and most effective at handling the overclock of the card. Powercolor's cooler had the most juice to deal with, with a vCore of 1.3v - significantly more than the other cards - but still managed to keep things under control. Noise was an issue for PowerColor, ASUS and HIS IceQ XTX - somewhat. All were much quieter than stock but became a little noisy under overclocked load. None are intrusive, and the HIS IceQ was a marvel of quiet cooling compared to the others.
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