As far as i know, the IO should be the same or less than VRam. If you overvolt the RAM to 2.0+ there's no reason for for the IO to be set so high. 2.0 should be plenty for the IO, but if you want some more MHz squeezed out out the RAM, you can take it a noch higher. If you adequetly cool your RAM, there should be no prob going up to 2.2V. Some people watercool the GPU and put heatsinks on the RAM, so it's not actively cooled. In this case i wouldn't go much higher than 2.0V. I have the case of stock HSF and the fan cooling the RAM and voltage regulators only, the waterblock is inside the HSF cooling the GPU. It's also touching the HSF, so it picks up some heat from there too. I used it for a few months already with 2.2VRam, and eveything if fine so far...I donno about the future, but hope it's not gonna burn out