I think I read somewhere that the video card has voltage regulators so that even if the agp voltage is cranked up, the card will only take so much voltage from the agp slot.
Also, the agp voltage is supposed to be linked to the ???Northbridge??? so by increasing it, you may be able to increase stability. I guess that's what you are achieving.
Now, it'd be greatly appreciated if someone could back me up on this or tell me that I've got it all wrong. Thanks.