Guru3d.com just this week posted the 2.0 Final build of Afterburner. It includes several new voltage tweaking features:http://downloads.guru3d.com/Afterburner-2.0.0-Final-download-2562.html
So make sure you upgrade to this latest version, and that should be all you need.
MSI Afterburner will not let me adjust voltages, I am using version 2.0.0 of Afterburner, and my cards driver is 70.04.13.00.01
I used nvidia inspector, but it only let me go up to 1.087 volts, < max temp I got with this was 72c in an Coolermaster HAF case with fan speed at %70) For what ever reason, I get artifacts past 850 mhz with that voltage. thanks to OvrClkr's link I am working out why.