After hours of tuning to see what the optimum voltage setting would be with best clock speed so I don't throttle the GPU and bring down the scores, I managed to stick with 1.5v on the GPU running at 1050MHz and 1200MHz on memory. I managed to obtain a total score of 17342 Mark, comprising of 19393 GPU Score and 13165 CPU score, so that's an extra 1587 points achieved by simply overclocking the GPU's.