First off you want to find the highest your CPU can actually go without the ram interfering. To do so you have to set the ram to the lowest possible speed, which is 100MHz or 200MHz as opposed to 200MHz and 400MHz effective. You might be thinking to yourself what does this have to do with anything? Well it has a lot to do with everything. Your ram is rated to run at 200MHz or 400MHz effective and it runs at a 1:1 with your CPU's HTT. This means that every time your raise the HTT frequency the ram frequency goes up. For example if everything is running at stock speeds (200:200) and you put the HTT up say 5MHz to 205 the ram follows at 205. The ram usually maxes out before the CPU ( in general, there are exceptions) and this is why you set it super low. The objective of this is to have the most efficient overclock possible. Say your CPU's HTT can go up to 265 but your ram maxes out at 245, you miss that much of an overclock. So now with the ram running at 100MHz and the HTT running at 200MHz you can put the HTT frequency all the way up to 300MHz knowing that whenever it doesnt post its your CPU and not your ram.
So to overclock your CPU you raise the HTT frequency slowly in 1-5MHz increments and adjust the voltage accordingly. You also have to adjust your HT frequency. You calculate the HT frequency by multiplying the HT frequency by the HTT frequency. You want to keep it as close as possible to 1000. At stock, 5 X 200 = 1000. You usually have a little bit a leeway like 1150 but not much more.
So now that youve found your max CPU speed you want to find out just how far your ram goes. Lets say your CPUs HTT maxed out at 270. We now know that, so lets start overclocking with the ram at 200MHz. Again do it in only 1-5MHz adjusting the ram voltage accordingly. Adjust everything that has to do with the CPU like you did before. For example you had to raise the voltage to 1.425V when the HTT hit 230. You do that until you have found your max ram STABLE ram speed. So lets say your ram maxes out at 235MHz but your CPUs HTT can go all the way up to 270. What do you do now? You use a ram divider.
A ram divider is simple. It runs your ram at a slower speed just like we did at the beginning. So now at this point setting the ram at 166MHz would be your best bet. So now the ram is running at 166MHz and your HTT is at 200MHz. So when you put your HTT frequency at 205 your ram will be running at 171MHz. So now when you set your HTT at 269 your ram will run at 235MHz. That is the most efficient overclock you can get.