Your board is a nVidia 680i LT chipset. Overclocking RAM on any nVidia chipset is a much easier proposition than any Intel solution as you can OC RAM independently of the CPU and not limited by memory dividers.
Overclocking RAM depends more upon the quality of the RAM being used than quantity of modules or density to a degree.
1Gb Dominator DDR2-800CL4 should overclock only fractionally better than 2Gb modules, while the 680i chipset has no difficulty maintaining voltage over four DIMM's for a 4x1Gb setup. Weak boards with iffy power delivery to the MCH (Northbridge) would favour a 2 DIMM setup but your board isn't one of them.
As for the OC, going for 3 GHz should be easily attainable on the board (333 Core freq x 9)
Stock cooler or aftermarket?
What stepping Q6600 ? B3 (sSpec SL9UM) or G0 (sSpec SLACR) ?
VID ?
Vcore in BIOS (if different) ?
For overclocking you will need some basic software tools-if you don't already have them.
Reporting utilities:
http://www.cpuid.com/cpuz.php (CPU-Z. Good basic info of your system)
http://www.almico.com/sfdownload.php (Speedfan-in depth voltage reporting)
http://www.softpedia.com/get/System/System-Info/MemSet.shtml (Memset. This utility will show you the pre-programmed RAM sub-timings within the modules, should you need to adjust timings from Auto in the BIOS )
Testing
RAM
Memtest86+ A DOS utility that will test RAM timings for stability outside of the OS enviroment) I've outlined the setup and testing procedure in this thread (2nd post)
https://www.techspot.com/vb/topic140759.html
CPU
OCCT : A good alrounder, you can test CPU, GPU VRAM, PSU. Each completed test will provide you with a graph like this:
Prime95 (32 or 64 bit): A very good CPU stress test. The blend (small+large FFT) torture test is usually seen as the true test of system stability
Stress Prime Orthos : SImilar to Prime95. Use one or the other
Intel Burn Test (IBT) : Stress test likely to show the highest CPU core temps you'll likely ever get.
OCCT, Prime95, IBT and Orthos here
http://files.extremeoverclocking.com/browse.php?c=18
You will no doubt come across people who tell you that such a small overclock that needs only a bump or two in the Vcore (and northbridge if OC'ing the RAM more than moderately) you don't need to stress the system too much -if at all. Quite simply, they are wrong, any setting on the computer should be stress tested for stability, including stock, because if you don't start from a basis of complete stability then any instability you encounter will not be able to be pinned down without going back to the start or a lot of trial and error.