Ok, well I removed my findings and the post above because they were incorrect, itsdanny's post made me go back, re-test a few things and double check my findings. So it turns out, here is what I found out now.
I had just been using Kombustor's reading of the core clock to tell if my card was throttling. This is not an accurate source of the actual clock speed and I should have been using GPUz. Now, using GPUz, I find out that both of my Gigabyte 6950 cards have been throttling all along. DOH :shadedshu
But I did still get some useful information from my research of two Gigabyte 6950s.
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First Finding:
Different 6950s use different VIDs for 3D voltage. Even the same model card from the same manufacturer. One of my Gigabyte 6950s uses VID3 and the other one uses VID4. So test your card to find out which one and make sure you are using the correct VID. This is also another good reason to edit and use your OWN card's bios rather than flashing a modified bios from another card to yours... even if it's the same manufacturer.
Second Finding:
A final explanation / bug of overclocking with Trixx. When overclocking with Trixx, even if your power control slider in CCC says +20%, that's not accurate and it may not be using +20% power causing your card to throttle down while gaming. You can confirm if your card is throttling by running Kombustor or Furmark while watching the GPU Mhz sensor in GPUz.
Here is the bug in Trixx. Trixx resets your Power Control to 0% each time you either restart your computer, or each time you change your clock speed in Trixx and click apply. Even though it resets your Power Control setting to 0%, your CCC still shows the slider as being at +20%. This is what fooled me. What you have to do, if you use Trixx, is this. Each time you restart your computer, or change your clock speeds in Trixx, you must open up CCC, move the Power Control slider down to something other than +20%, click apply, then move it back to +20% and click apply again. It's a little tricky because you only have 1 second to click apply before the slider goes back to whatever it was. Another way of doing it is to close Trixx, then open CCC, set Power Control to anything other than +20%, apply, then set it at +20% and hit apply. After that re-open Trixx. This way you don't have to fight with Trixx moving the slider every 1 second.
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