Good, 3DMark06 is a flawed benchmark due to the CPU test though, newer games are much more GPU bound and an ultra high end quad won't give better performance than your E8400. I scored 14800 with my rig below and 15700 during the couple of days that I was running a G92 8800GTS.
Just determine you max overclock by increasing only one clock at a time. Start with the core clock, and increase in 25MHz increments running stability tests in between. When you have determined the max speed for the core, you can move on to the memory and repeat the process. I recommend using Rivatuner.