the source of confusion here is that there are two different numbers commly interchanged in relation to FSB. The frequency, and the DDR (double data rate) frequency. If you set your FSB at 166 it is "really" running at 333. If you set it at 200 it is "really" running 400mhz after DDR is taken into consideration.
The way it works is you are running a frequency of 166mhz, or 166 million cycles per second. Now the way DDR works is it uses both the rise and the fall of the clock cycle (electrical pusles) to transmitt data, thereby getting twice the bandwidth out of that 166mhz.
The 6:5 ration part is the ratio of your memory FSB speed to your processor FSB speed. The memory is running at 166, the processor is running at 200. 200/166 is approximentally 6/5. Generally the best performance is gained fron running them at the same frequencey (1:1), but in your case that may not be because you wont be able to get your CPU up to where it should be by doing so.
Now in regards to dammaging your system, no. Going above and beyond the rated specs is called overclocking
... its what we do here
. Now, that said, it CAN cause dammage when coupled with insufficient cooling and too much voltage, and it can shorten component life, though not significantly. Just be careful, watch the temps at first, and dont up the voltage too much.
