Is it PC 3200 RAM? If it is then do this. Download CPU-Z from http://www.cpuid.com
and open it up. Then look at the SPD tab to see what your timings should be at for it to operate at 200 MHz. Then you'll have to go into the BIOS and change the timings. With a 5:6 ratio, the RAM should be able to function at at least 200 MHz, so make your "max memclock" 166 (that simply means a ratio of 166:200). Then put your timings at what it should be according to the SPD chart. Write them down if you can't remember the name and timing associated with each name. After you make the adjustment (if you plan on doing this) let us know how it panned out for you.
If your RAM is not 200 MHz (DDR 400, PC 3200), then don't do this. Tell us what your RAM is.