Which Memory to buy for optimal performance?

I’m looking for a little bit of education with regards to CPU fsb and memory speeds, as I’m not sure what memory to pair with a motherboard and CPU.

Some of the mobos I’m looking at support the following:

CPU: 1066/800/533 fsb
Memory: DDR2 800/667/533

My thinking, and I’m sure I’m probably wrong, is that ideally you want to match the CPU and memory fsb 1:1, or integer multiples of each other 2:1.

The reason behind my asking is that instead of running the system at 800/800 cas-5, I wanted to save a few $$$ by running it in 1066/533 cas-3. The CPU I have in mind is the Conroe E6600, and the memory will be 2x1GB

Is there anything inherently stupid in doing this? Will the lower latency help make up for the 2:1 ratio? Will there be a huge system impact? Keeping in mind that the system will at first be used to play RTS games (no first person shooters), and eventually make its way into a Home Theatre PC. Also, I have no intention of OC the system.

Thanks for your help.

Oh the great fsb and memory speed question.

Ok first some background:
Intel has a quad-data pumped bus. This means that it transfers 4 pieces of data for every clock cycle. Hence, since marketing folk like bigger numbers, the numbers you see on the motherboard/CPU are the (real bus speed * 4).

So this means that the real bus speed for 1066Mhz is 266Mhz, 800Mhz is 200Mhz, and 533Mhz is 133Mhz. Just divide by 4, see?

Now memory. DDR2 means Double Data Rate. Its long name is DDR2 SDRAM. The "2" stands for 2nd generation, I assume. Remember that DDR (1st generation) is not equivalent to DDR2!

Since its DOUBLE data rate, the speeds you see on the RAM are (real bus speed * 2). So 533Mhz is 266Mhz. 667Mhz is 333Mhz, 800Mhz is 400Mhz.

Now the kicker. Since you're NOT overclocking, you don't need anything beyond DDR2 533Mhz. Why? Because overclocking means (at least for locked CPU multipliers) raising the real speed of the FSB. So theoretically, having 667Mhz DDR2 memory would let you raise the FSB's real speed to up to 333Mhz.
More on overclocking at the sticky here:
http://forumz.tomshardware.com/har [...] 97995.html

As for timing, its not going to make big difference between CAS 4 or 5 or 3. Single digit percentage points is all. Personally I'd just get CAS 4 or 5.

If I screwed anything up, please feel free to correct me.