You sure it wasn't a DX9 vs DX10 thing? DX10 is faster than DX9 so long as all the settings are the same (and usually, they're not).
Quite sure, as TrackMania is a DX9 game. I used it, because it has a really easy to use and repeatable benchmark mode that doesn't take very long to run.
Anyway, I've now received the results spreadsheet from my friend and attached it to this post. It was about a year ago we did this, so it's XP SP3 v Vista SP1. Both operating systems were 32-bit and fully patched, had the latest DX update and drivers applied.
We tested a HD3850 512MB & a HD4870 512MB on an E8400 at the stock 3GHz. The performance loss with Vista averaged a large 30%, with the 4870 actually taking a bigger hit.
Windows 7 isn't any better, either. I did a couple of bench quickies with Windows 7 recently and the results don't change much. nvidia takes a slightly smaller hit, if I remember correctly, but I didn't bother to write the results down.
In short, if you want the best DX9 gaming performance, stick to XP 32-bit and that applies to the latest hardware, too. Our friend Aleksander Dishnica is right when he says he gets better 3D performance on XP.
The Athlon 64 results are there to quantify just how much faster the E8400 is compared to the Athlon 64. As you can see, it's way faster, as you'd expect. Interestingly, you can see how the system with the faster CPU & slower graphics card can sometimes beat the system with the slower CPU & faster graphics card, depending on the exact bench parameters.
Oh and finally, TrackMania is awesome.