So finally I put together a standardized graphical benchmark with aspects for all users. And no, it won't output a single number, because that would be meaningless for everybody. But it makes it easy to compare different aspects between different graphics cards and drivers, and there are some surprising results. But more about the results later.
The sources for the benchmark are now on gitorious, and the Wiki entry describes its usage. It's currently somewhat tailored to SLE11SP1, so you might run into minor issues when running it on a different OS version. And of course, it's not very polished yet .