After flashing the Cayman Pro, we were able to use all 24 SIMD and gained the stock clocks of the Cayman XT. To successfully run benchmarks and other tests, we needed to adjust Power Tune to +15%. To gain some perspective on what the unlock provides, we compared the performance of the HD 6950 in stock, overclocked, and unlocked form against a standard HD 6970. We also included overclocked results for the unlocked Pro, and for the original XT. We used four benchmark tests: 3DMark11 Performance mode, Aliens Vs. Predator benchmark, Lost Planet 2 benchmark B and S.T.A.L.K.E.R.: Call of Pripyat benchmark. The results are below, mouse over for more details.
Results of 3DMark11's new Performance mode, using -20, 0, and +20% power tune settings, for both Radeon HD 6950 and HD 6970 at stock clocks, and in HD 6970 Crossfire.
Aliens Vs. Predator
FRAPS recording results of Aliens Vs. Predator benchmark at 1920x1080 with 4xFSAA/16xAF, Very High textures, High quality Shadows with Advanced Shadow sampling enabled, SSAO and tessellation enabled.
Lost Planet 2
FRAPS recording results of Lost Planet 2 benchmark B (DX11) at 1920x1080 with 4xAA, highest settings.
S.T.A.L.K.E.R.: Call of Pripyat
Sun Shafts preset benchmark result, running at 1920x1080 with Ultra preset, 4xAA, default SSAO, 10.0 style Alpha, contact hardening shadows, tessellation.
System power consumption under Windows 7 desktop idle and 3DMark11 load.
GPU Temperature at Windows 7 desktop idle and 3DMark11 Graphics Test (Extreme preset) 2 load.
The results generally indicate that you get a little more performance by unlocking and running at XT speeds than by running at higher clocks in Pro configuration. Unlocking and overclocking yields the best result, although you may need to tweak PowerTune to find the best balance for long term stability; we found sometimes that +15% would offer more stability than +20%, apparently nudging the power delivery can push the limits of the card.
If you have a Radeon HD 6950 and aren't afraid of possibly trashing it, then the unlock is a free performance boost of significant proportions offering significant savings over a HD 6970 or a GTX 570. A fully certified Radeon HD 6970 is likely to overclock further, and has more headroom for delivering power if you decide to increase core voltage. You also get the full complement of texture units, and the 6Gbps RAM for more memory bandwidth. If you're the kind of tweaker that likes to go all out, remember that at least in part, AMD bins these chips for a reason; they might not make the grade for a HD 6970.
Currently, only ASUS cards feature voltage adjustment using SMART Doctor. If you want to take an AMD Radeon HD 6900 series to the limit, then your best option right now is to buy an ASUS Radeon HD 6950 or flash to an ASUS BIOS and use their software. The very bravest could try replacing the 6-pin power input with an 8-pin one, or bridging the two vacant pins to the installed 6-pin input's ground connections, but it's unknown if this would have any benefit - PowerTune may still operate as if the board were 225W equipped, and it's a very risky operation.
Cayman PRO - AMD Radeon HD 6950
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