Okay, it's partly because if the RAM/CPU ratio is at 1:1, the RAM processes the information sent by the CPU exactly. In this case, neither the CPU sends more the RAM can handle, or the RAM stays partly idle, because the CPU is sending less the RAM can handle. Basically you even the matter. The CPU sends - the RAM processes.
Also, this allows your overclock to go higher. Let's say, for instance, you have a higher RAM than CPU ratio, then your RAM frequency would be higher. If your RAM isn't overclocking friendly by X or Y reason, then you would be stuck. So you "lower" the RAM frequency (which is good in your case, as it's a 1:1 divider, the best divider for Intel CPU's) and your RAM can be squeezed more. If the RAM is your obstacle in your overclock, then you can gain more speed.
For example, in a old P4 2.4A I had, I went to 3.0Ghz on a Higher RAM than CPU divider. I made the divider 1:1 and I could get to around 3.3 Ghz. So it definitly does matter, and it makes the CPU work better in my opinion.
Originally Posted by the Intel Overclocking Guide
On Intel systems, best performance is achieved through highest possible stable operation in synchronous (1:1) CPU:RAM operation. The higher the FSB in 1:1, the better performance. The only exception may be if you have severely limiting RAM and a CPU that is an excellent overclocker. That is up to you to determine, tho. Does a 5:4 divider at a super high CPU clock offer better performance than half the FSB in 1:1? Well then, stick with 5:4. At the same time, running RAM faster than the CPU offers absolutely no performance gains (the CPU is doing the processing, RAM merely receives data as it is fed to it...). I don’t know why motherboard manufacturers even offer dividers to run RAM faster than the CPU, but they do. So, please, for my sake, don’t go setting your CPU bus speed to 133 mhz and DRAM frequency to 200 mhz (or 400 mhz, depending on how your BIOS lists it).
EDIT: If you want to find your 1:1 Divider, just multiply your FSB by 2 and select that number in DDR Frequency.
EDIT2: Damn, double post.