Overclocking is rarely a good idea imho. It can leads to failures. Adding RAM would be useful if your motherboard can host more. For my own, I am stuck with 8GB on my old Asus P5K and it is not enough to fill my GTX 580 3GB without using the swap on disk : it gives very long exporting time due to constant disk acces. 16 GB would help, but on some scenes, Windows ressource manager shows that more than 17GB is required. 24 GB would be comfortable.
French Blender user - CPU : intel Quad QX9650 at 3GHz - 8GB of RAM - Windows 7 Pro 64 bits. Display GPU : GeForce GTX 480 (2 Samsung 2443BW-1920x1600 monitors). External GPUs : two EVGA GTX 580 3GB in a Cubix GPU-Xpander Pro 2. NVidia Driver : 368.22.