Complicated subject, IMO. You may want to read http://www.tomshardware.com/reviews/pc-memory,1698.html
General info taken from http://www.hardwareanalysis.com/content/topic/34949/CPU Clock
The very first setting that needs to be made in the BIOS is to adjust the motherboard to utilizing the proper clock settings for the CPU installed in the computer. Most modern BIOS vendors can detect the type of CPU and automatically set the proper timings. Refer to the documentation from the CPU and motherboard vendor for the proper settings.
The CPU speed is comprised of two numbers, a bus speed and a multiplier. The bus speed is the tricky part because vendors may have this setting done either at the natural clock rate or at the enhanced clock rate. The natural front side bus is the more common of the two. The multiplier is then used to determine the final clock speed based on the bus speed of the processor. Set this to the appropriate multiple for the final clock speed of the processor.
For an example, if you have an AMD Athlon XP 2500+ processor that has a CPU speed of 1.82GHz clock, the proper settings for the BIOS would be a bus speed of 166MHz and a multiplier of 11. (166MHz x 11 = 1.826 GHz) Memory Timings
The next aspect of the BIOS that needs adjusting is the memory timings. Typically it is not necessary for this to be done if the BIOS can detect the settings from the SPD on the memory modules. In fact, if the BIOS has a SPD setting for the memory, this should be used for the highest stability with the computer. Other than this, the memory bus is the setting you will likely need to set. Verifying that the memory bus is set to the appropriate speed for the memory. This may be listed as the actual MHZ speed rating or it may be a percentage of the bus speed. Check with your motherboard manual about the proper methods for setting the timings for memory.
My thoughts: Instability may occur by changing either one of these (trial-and-error will show this), but...as long as the user is able to get back into the BIOS to reset...I see no harm is experimenting. Then you will know.