Which G31 motherboard? If Gigabyte, I can give you some OC suggestions.
You should be able to reach around 3.5 - 3.6 GHz or so. Some samples of the E5200 series chips can reach 4 GHz. THe best that I have been able to do with an E5200 is a little over 3.75 GHz.
The G31 is an economy chipset will an upper FSB limit of about 350 MHz. The E5200 series is a pretty good candidate for overclocking because the FSB is so low (200 MHz) and the internal multiplier is, for a Core2 CPU, so high. That combination means the motherboard or memory will not be the limiting factor.
I have no idea how far you can push the chip using the stock heatsink. That will depend on load temps. With a Hiper 212+, you will likely be able to reach a max of 1.45 volts before you reach Intel's recommended max load temp of a little over 70 C.