For one, never use auto setting you'll never be able to reach an overclock..

Secondly your NB voltage is not that sensitive to heat comparable to your CPU
So raise your CPU Volts as you cant be stable in windows and after you've gone two voltage steps in your BIOS i would give .05v to your NB, im not sure how the P5b BIOS is if its in .1v increments or .05 or what, but i would just go up one each time..

if you plan on going to 3.0, i would suggest not neading more than .2V to your NB and nothing over 1.475 to your vcore