Various Experimentation: Geforce 8400 and Celeron D 356 ES
As you can see, after raising my PCI-e voltage .1v up to 1.6v, I managed to pull about 115MHz more out of the GPU and a few MHz more out of the memory. I would've went higher on the GPU, but afterburner actually wouldn't let me go any higher. The slider just wouldn't go any farther. Any advice is appreciated. I also raised the PCI-e frequency to 100MHz in the BIOS (from 90, I think). I don't think it makes much of a difference, though.
As you can also see, I got my Celeron D up to 4.75GHz @ 1.6v VCore. My temps were out of control when I first tried, but it turned out that since I have my heatsink taped down it needed more thermal paste to make adequate contact. THAT's another story. ;)