That board supports up to 95W CPUs. Q9650 is the fastest. O/C depends on whether your BIOS allows it. Basically you raise FSB, check temperature, Raise voltage , raise FSB, check temp. Improve cooling , raise FSB and voltage, check temps. When you run out of volts,FSB or cooling you're done.
With a locked BIOS there are other methods. Software like Clockgen, SetFSB, and Throttlestop have their uses. Pinmods called BSEL, and VID are used also. A lot of people including myself do the cooling mods first. Stress testing and benchmarking are used to check the usefulness of your results.