Overclocking any PC component can drastically increase the performance of your computer. Although the processor is the most commonly overclocked component, you can also overclock a graphics card, or memory. Overclocking any component can be difficult and very risky, but there are three ways of doing this so you can choose the best way to suit your needs. Hardware is the most difficult and riskiest but it can provide the best results. Using your BIOS is slightly easier but not all motherboards support it, and software is the easiest but also doesn't deliver as high results.
Riva Tuner Driver For Mac Pro
Using free software such as Riva Tuner can provide instant results however, greatly increasing the performance of your graphics card. Link to RivaTuner Website.