There is no difference between running on Linux (with GL) and Windows (with Direct3D9).
At least from what I've seen on my hardware with Win7 and the same build on Kubuntu. And generally IMO there shouldn't be a difference (on same hardware).
Shader model is just something that is directly connected to GPU (its core). Generally SM 3.0 is present in all recent GPUs since few years (I think more than 5 years).
Next, I've wrote which GPUs I have, here on
hardware requriements. So, on my GTX 560 Ti, I get 60 fps on big tracks and about 90 or more on smaller, using Higher preset (default) and without any effects.
Then, as for the cards, I compared with some benchmarked values,
from
this site (And I'm guessing now that this list would have all of the cards that can handle the game well):
GTX 560 Ti - 3530 (my primary, Higher preset, >60 fps)
GT 640 - 1292 (my second gpu, didn't test on it a while, but should do 40 fps on High or so)
9600 GT - 753 (so called "minimal requirements")
8600 GTS - 307 (probably less than 9500 GT I hope)
Not sure if anyhow useful, links to compare GPUs:
GT 640 vs GTX 560 Ti,
9500 GT vs GTX 560 Ti.
So I think if you see your GPU
here (high) (or
here (low)), read the benchmark value and simply dividing it with those above will tell you how well should it perform.
I'm not sure, but basing on those values, your card would do 10x less than mine, 4x less than my worse, and about 2,4x less than "minimal requirements". No idea if this is true. I would start trying Lowest, Low and maybe medium settings. See how it does. But 30 fps is probably max to have with it (on medium tracks?).
Yeah, I should probably decrease the difficulty for Infinity, few people already said that it's not so difficult.