Test results
Starting with some 3DMark05 runs.
Both cards scale in a uniform fashion, overclocked or otherwise. The 6800 GT benefits more from its slightly more fruitful overclock, but not by much more than the PixelView 7800 GTX. In this synthetic benchmark then, there's a decent performance gain to be had from plunging for the PixelView.
Turn up the anti-aliasing and anisotropic filtering, which is what you'll want to be doing in your games, and the graph shifts downwards by about 1000 points, all cards and clocks taking a hit.
Moving on to the darkest depths of the Doom III timedemo:
Here we see what happens when the rest of your system can't keep up with your graphics card. Both cards seem system-bound at 800x600 and even 1024x768. If 1280x1024 is your max res then the 7800 GTX will be left wanting more.
Go for some quality enhancements and the graph spreads out a little more. Want high res, high image quality Doom III gaming? 7800 GTX is 25% faster than the 6800 GT, in this system at least.
Gordon's turn, now.
Another example of the system holding the 7800 GTX back.
The GeForce 6800 GT starts to slip, but still remains very much playable. The PixelView 7800 GTX laps it up.
So, from this little snapshot of benchmarks we've got pretty much what you'd expect. The test system restricts the review card much of time. However, get up to the resolution at which most of you will want to play games, and it's clear that you can afford to have plenty of graphical niceties enabled.