NVIDIA Benchmark Results
Far Cry
There's very little performance difference whether PEG Link Mode was enabled for the NVIDIA 6800 Ultra or not. All in all, there was only a variance of about 2%.
Both Normal and Slow modes were completely tied in performance. When it was set to Fast, we saw an minuscule increase of 0.5 fps or 2% over the Slow/Normal modes.
Oddly, increasing the PEG Link Mode to Faster did not make it faster. In fact, the card became slightly slower than when PEG Link Mode was set to Fast.
The Auto setting took the cake for being the slowest in this test. In fact, it was slower than even the Slow setting!
Doom 3
Things were a little different in Doom 3. Slow was noticeably the slowest setting at 37.40 fps. Setting PEG Link Mode to Normal, Fast or Auto boosted the card's performance by 1 fps or 2.7%.
But the fastest setting was Faster. Setting PEG Link Mode to Faster improved the card's performance by 0.1 fps, which is really imperceptible. So, it is essentially just as fast as the other PEG Link Modes (except Slow, of course!).
Counter Strike : Source
In CS : Source, Slow was, once again, the slowest setting. But the variance between its performance and that of the fastest setting is only 2%.
Setting PEG Link Mode to Normal gave the card a 1.5 fps boost over that of Slow. but increasing it to Fast actually dropped it slightly by 0.5 fps. The Faster option proved to be slightly faster - being 1.55 fps faster than the Slow setting.
But the fastest setting was, oddly enough, Auto. It garnered the highest frame rate which was about 1.6 fps faster than the Slow setting.