The Lightningís purpose in life is to be overclocked and despite it arriving with a factory overclock, it would be a crime to not push it further given that it is equipped with the best components available. Long story short, the Lightning lived up to its name and MSIís claims. Even when looking at the factory default clocks, our expectations grew. At 940MHz on the GPU, the clock speed already represents a healthy 7% boost over the reference clock speed of 880MHz. Unlike ASUSís bold claims of providing pre-overclocked cards that turn out to only have a measly 10MHz overclock applied, MSIís do not disappoint and moreover, their factory set clock is close to the final speed we managed to achieve on the reference card. Best of all, the pre-overclock of 940/5500MHz was done on the stock voltage of 1.175V rather than at 1.25V as was the case with the reference card. This demonstrates the confidence MSI have in their product and the custom cardís ability to sustain greater stress. If that wasnít enough, MSI have also reported to us that retail versions of the R6970 Lightning will boast an even more impressive 970/5500MHz factory set speed. Unfortunately, the memory was left untouched despite being rated for 6Gbps. At idle, the card operates at 1.0V and clocks down to 500/5500MHz when using dual screens. Otherwise it clocks down further to 175/300MHz to save even more power.
Overclocking as expected was fairly easy despite the initial factory clock already taking a lot of the headroom on the Cayman GPU. Using MSIís own brilliant Afterburner application, the GPU core voltage was set to 1.3V and additionally, the software allowed the memory and auxiliary voltages to be altered. The former was increased by 10mV and the latter set to 1.179V to further increase the cardís headroom. In the end, an impressive 1010/6000MHz clock speed was achieved! Breaking the 1GHz barrier is no easy feat on any graphics cards and given my previous experience with reference HD6970s, I secretly doubted whether the Lightning could pull it off but it did. The core clock represents a 7.4% increase over the factory set 940MHz and a 14.8% increase over reference AMD clocks. It is also possible to go further using the on-board dip switches or the BIOS switch to remove the memory headroom limit but unfortunately the switch on our sample didnít function properly. The downside of overclocking the Lightning is its power consumption which we will investigate later. When overclocked, the GPU still idles at 500MHz but the voltage doesnít decrease.
The pre-overclocked Lightning has some very impressive specifications above the reference card and the fully overclocked card takes the HD6970 to new levels of performance, on paper at least. The overclock translates to the same percentage gains in fill rate and shader operations while the memory bandwidth has also increased by 9% to reflect the 500MHz overclock.
The 7.4% overclock on the Lightning translates to an overall 5.23% performance gain in the real world. This isnít a linear as I would have hoped but the result is more favourable than that of the ASUS DirectCU II HD6950, suggesting that PowerTune was not throttling the cardís potential as much.
Another highlight of the MSI R6970 Lightning is of course the Twin Frozr III cooler. At stock factory speeds, it yields very impressive temperature deltas, in this case only bested by ASUSís DirectCU cooler. However, it is important to remember that the Cayman based HD6970 runs much hotter than the GPUs being cooled by ASUSís cooler and the fact that the Lightning sports a much higher relative overclock is testament to the Twin Frozrís cooling ability. Compared to the reference AMD vapour chamber cooler, the Twin Frozr III ran 13C cooler. This does not match MSIís claims of their card running 26C cooler but it was compensated by quieter operation. At idle the fans operated at a mere 39%, ramping up to 58% under load. The fans were inaudible under 55% where they produced a gentle hum. They only became intrusive at 70% but the low pitch made it very bearable and easily drowned by games.
When overclocked with 1.3V coursing through the GPUís circuitry, the load delta temperature increased to 66C, still a few degrees below the reference cooler. Bizarrely, the fans went into overdrive and reached 95% rotational speed but thankfully the noise was still bearable. The extra performance comes at the cost of noise but not enough to detract it from its quality. As a dual slot cooling solution, thereís no doubting that the Twin Frozr III is amongst the best custom coolers available.