To address this question of multi-platform compatibility, the Phoronix Test Suite software is compatible with Solaris and I'd anticipate it even working on the *BSDs.
I suggest you a crossplatform test. Not all the benchmark - better if they are -, but at least a part of it.
If the same test can be run over windows / Linux / MacOS / and others with a single number score, It would be better.
Then the driver development across the time and systems would be better, at least to watch.
For example a KDE4 test (it is cross-platform), and some similar as VLC tests for videos, Quake tests for games etc.
Opengl test would be a great tool to compare between drivers and systems.
We will find that, best sysmark - only windows - results may be not best with Linux or Mac OS.
And perhaps in a future some systems under Linux score high than under windows with driver improvements, especially for games.
I should put office tests with openoffice, browser tests with Firefox and opera, and of course on that tests Linux and MacOS should win windows, HD and RAM ones probably too. The lack are graphic drivers, and ATI and NVIDIA are working well now opening their drivers, but it is not enough.
I wish this benchmark become a world reference one for non directx benchmarks for every OS.
I would like to see your scores at any other computer analitics web page, as anandtech, tom's hardware, extremetech, 4gamers and similars.