I'm looking to create a list of graphics cards which have voltage regulator modules (VRMs) that can't/don't allow the graphics card to increase voltage. I want to help people who, like me, buy a GTX/HD xxxx hoping to overclock it to it's full potential but then finding that they can't increase the voltage to get more out of the card. In my case I purchased two Gigabyte 6850s Factory overclocked. Despite being clocked slightly faster on installation, it's impossible to overclock much further because Gigabyte made sacrifices on the VRM to make so they could sell the card for less money. However isn't it slightly ironic that the standard version of the card can have it's voltage increased and therefore makes a much better overclocker?
So I just want to help people by compiling this list so that people don't run straight into a shop and pick up a factory overclocked card that could be worse than its standard sibling. I'll add mine to the list first.
By no means are all of these cards bad, but if you're into overclocking you might be better off with a card that allows it's voltage to be increased.
Cards with Locked Voltage:
Gigabyte Radeon HD 6850 Overclocked Edition - GV-R6850OC-1GD
Thought I couldnt either with my gigabyte 560ti's, but in MSI Afterburner advanced settings you can select unlock Core voltage and change the Core voltage settings via the slider
Have a look and try it yourself, should work for you too.