The 8500 had 275mhz clock on Memory and GPU. The 9200 had 240mhz clock and 200mhz ram. Also it had a more complex pipeline arrangement (4/2:2 for the 8500 vs 4/1:1 for the 9200.. whatever that means) and the 128meg version had it's memory interweaved which probably did a slight performance boost.)
With 7500 I donno. I expect their would be 3d acceleration from Free drivers, but it's probably been a long time since anybody tried to use them for gaming so I don't know of the stability.
ATI was somewhat helpfull with 3d drivers in Linux up until the time right around they won the contract to start developing a GPU for the Xbox 360. It is probably a coincidence, but maybe not. It's the same time frame anyways. Now a X developer has made 2D drivers for the r500 series cards and ATI has him under NDA because of what he does for a living and they are refusing to let him release code for those, even though they are very basic drivers.
It's probably just normal corporate BS. Everybody is too chicken to actually say 'yes' to anything.
Well, opensource drivers don't normally influence me of my next purchase. Competent drivers do influence my decisions. So if the Intel 965G can outpace my X800 Pro 256... then I'd gladly buy one mobo from Intel.
(anyways.. If it was raw speed your after both your ATI card and the majority of your games would run much better under Windows, so why bother with Linux? (we both know it's more then just speed))
I am doubting that the X3000 will even been that much better then the GMA 950 at this point. It'll probably help in those games that take advantage of the extra hardware features that X3000, but otherwise I'd bet it's a incremental increase in performance, not a huge one.