if you use manual GTL Ref multipliers , then you need to change these periodically as you go between higher and lower voltages across different FSB/DRAM/CPU clock frequencies. Different clock speeds will sometimes need more or less GTL_REF voltage depending on how the signal quality is at that point. I've found myself adjusting them as I've been down adjusting voltages to find stable voltages for current 8x445FSB and 3.57GHz cpu. But got a DRAM timing issue which I can't put my finger on, I've changed too many timings too loosely and seems like I've caused at least one minimum time period to be too short. tRAS or tRFC, guess I'll know which once I finish making sense of all the timings and their minimum values. DDR timings are too damn many, and confusing. Lack of collective data mostly, I've got so many data sheets and white papers I'm sorting through today on the way to making sense of all the different names used by manufacturers.