I installed the latest version of Evga Precision X application to overclock the 2GB GT 640 GC. The stock clocks for this card are 950/1,782 and I was able to increase them to 1,180/2,082 (offsets of 230 and 150) after increasing the voltage from 1,050mV to 1,113mV. I did increase the fan speed to 75% since I noticed the auto setting would never increase the fan speed over 55%. This overclock represents a 24.21% increase in the core clock speed, and 16.83% increase in the memory clock speed.
The custom cooling solution kept the GPU to 50 degrees Celsius and under even with the increased voltage and overclock. Even with the fan turned up to 100% I never heard it over the other fans in the machine. According to Galaxy the maximum load temperature is 56 degrees and the maximum noise level is 29.3dB.
The Unigine Heaven Benchmark is a very well featured benchmark designed for testing DirectX 11 performance. The benchmark winds the camera through a beautiful floating island that has been designed to show the amazing detail that can be built into a properly designed DirectX 11 game.
The tessellation level was changed between moderate, normal and extreme and the other settings were as follows:
The performance of the GT 640 at stock speeds and overclocked speeds were nearly identical at the moderate and normal tessellation levels. At the extreme tessellation setting, the graphics card was actually taxed and then made use of the overclock.