Went to bios and bumped the speed to 3.6ghz, stock volts and Stability tests are fine. I bumped to 3.75ghz, now it's unstable so I increased the voltage from the stock 1.25 to 1.325 (this is the max "safe" operating voltage as specified by intel). I ran prime again and it's still unstable, sometimes it wont even boot to windows. I tried again 3.6ghz with 1.325v and ran prime and some monitoring programs. Stable, but I noticed that the HWmonitor and cpu-z indicate that the cpu voltage is only 1.2v even though it's 1.325 in my bios. How come? I want to increase my speed but cant because something is limiting my voltage to 1.2v. This isn't even the default voltage of 1.25.
Who do you trust? Your motherboard bios may be correct. Have you disabled all settings related to energy conservation in the bios? Eist (speedstep) is only one of several settings that may be limiting your voltage. Check your settings again to be sure.
The g31 boards are low budget, not designed for overclocking. If you want to go higher, I suggest you checkout some bios settings in a p45 board. You can download them off the manufacturer's website and decide if it's worth changing motherboards. DFI usually has the most bios options for overclocking.
Then you've done your best. If you are still not satisfied, you can sell your cpu free on craigslist and try another one. I use the i3 530, and it's running stable with the Intel heatsink at 3.67. At 4.07 it runs but too warm for the Intel heatsink. I settled for the lower overclock rather than buy a pricey heatsink. I got both the board and cpu for $100 after rebate at frys.