Trouble OCing sempron 2500+

Hi I am having trouble oveclocking my Socket A sempron 2500+
I Can't seem to keep it stable. I am currently stable at 1900MHz (181x10.5) @ 1.66 volts. I have tried pushing the FSB to 185/190/200 with no luck. I have had my voltage as high as 1.7 Volts. How much voltage can this chip withstand running 24/7? My current temperatures are 38'C Idle and 44'C Full load. Im using a thermaltake volcanoe 12 and Arctic Silver 5 thermal compound. The fan is at 4000 of 5600RPM. Case temp idle 25'C Full 29'C.

I ran 2v through my AXP system on water for a few months 24/7 before local construction sent a surge through my house, killing several pieces of equipment... yes, you guessed it, including my PC. Before that I had run 1.9v through my AXP on air for a few months. Try 1.8 & see what it'll do & then inch up the voltage up from there until you see no gains. My guess is the NF7S2 won't give you much more than 1.9v at most. Keep your temps at or under 60° at load. Lower temps are always preferable, especially when running "high" voltage through your chip.

Ive just noticed that im getting a bit of voltage fluctuation on my Vcore. Its fluctuating between 1.648 and 1.664 Volts. Im thinking this is what might be causing the instability problems at higher frequancies. (The Vcore is set to 1.65V in bios.)
Could this be the problem?