it really depends on the GPU's chip. Both the AMD and Nvidia manufactured chips can very in quality. This affects the OC of the chips. Every GPU will very in the ability to OC. Best advice, download the overclocking software from the manufactures website and try pushing the core and memory speed. Watch the Temps and keep them within acceptable limits. This is the most important thing in overclocking, keeping the temp down, so you don't have throttling and damage to the chip.