I use riva tuner & ati tool to OC my system, but it puts a strain on CPU's & extra cooling is needed as the run a bit hotter if OC'd too much.
The GPU in my graphics card is already factory OC'd & 4GB of dedicated & 2GB of hyper memory - 6GB of gaming memory is enough I think, well its more than a PS3!!
Here its specs from wiki:
The PlayStation 3 uses the Sony, Toshiba, IBM-designed Cell microprocessor as its CPU, which is made up of one 3.2 GHz PowerPC-based "Power Processing Element" (PPE) and eight Synergistic Processing Elements (SPEs).[52] The eighth SPE is disabled to improve chip yields.[53][54] Only six of the seven SPEs are accessible to developers as the seventh SPE is reserved by the console's operating system.[54] Graphics processing is handled by the NVIDIA RSX 'Reality Synthesizer', which can output resolutions from 480i/576i SD up to 1080p HD.[47] The PlayStation 3 has 256 MB of XDR DRAM main memory and 256 MB of GDDR3 video memory for the RSX.[55]
Pretty poor when you compare it to a pc
