Here is a link from a Gskill forum.
They want their ram to run at 2/3 the CPU-Northbridge frequency. I'm running my 4 year old MSI board with a Phenom II x 4 980 BE, and I have 16 gb of Gskill Ares ram. I have my fsb standard at 200, my NB multiplier at 12 so my CPU-NB frequency is 2400, and my fsb to ram speed ratio at 1:4. That gives me a 1600 ram speed with the ratios Gskill advises.. They recommend increasing the CPU-NB voltage by .05 for that, and by .1 if you're going for 1866 ram speed. So I raised mine by 05. To get 1866 ram speed with a 1:4 fsb to ram speed ratio on my old mb I would need to up my fsb to 234. I do have 8gb of Gskill 1866 ram, but I would need to run my CPU-NB frequency at 2800, and I'm concerned about upping my CPU-NB voltage necessary to achieve stability. I just don't want to fry my cpu. Right now my system crashes at a CPU-NB frequency of 2600. Perhaps I'm conservative. I also have an older board, and don't know if the fsb to ram speed ratios have gone above 1:4. Even if they have, you would still need your CPU-NB frequency at 2800 to achieve the 1866 ram speed. However, you could do that with a fsb of 200, a 14 Northbridge multiplier and a 1:4.66 fsb to ram speed ratio.
Since setting those parameters, I decided to OC everything by increasing my fsb speed by 3%, taking it up to 206. I am concerned at what point I will exceed the timing on the ram. My Gskill Ares timing is 9, 9, 9, 24. The timing on their 1866 ram is 9, 10, 9, 28. That would be my next adjustment if I wanted to further oc my 1600 rated ram. I'm thinking about taking my CPU-NB frequency up to 2592 by increasing my fsb to 216, which would give me a ram speed of 1728, or an 8% OC. I don't know if my 16 gb of 1600 ram will be happy at that, or if it is better to put the 8gb of 1866 ram in and run it below its rating. I'm also concerned that the gains from the additional ram speed would be lost with the slower timing settings.
I am also overclocking my cpu with the multiplier. Stock is 18.5, and I'm running it at 19.5 giving me 4.07 Ghz. I would probably drop it .5 if I further OC my ram by increasing my fsb to 216. I hate to OC over 10%, thinking it will shorten the life of the components. I will probably upgrade my mb when the new MSI 990FXA gaming board is released, so I have SATA III to get the full benefit of my new Samsung SSD. I currently have an MSI 790FX-GD70, which runs like a champ but is a SATA II board. Perhaps that is my best move to improve the performance of my system instead of toying with my ram. It will probably handle a 2800 CPU-NB frequency, and I can run my 1866 ram stock. However, with these settings my old rig is quick: WIE cpu of 7.5, and ram of 7.7.