I just ran a few tests of a brief demo of graphics intensive pub play and got surprising results
DX9
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dx9frames:73.60 fps 8.985 fps variability
maxframes: 76.16 fps 8.953 fps variability
highframes: 62.94 fps 7.651 fps variability
default: 115.47 fps 8.673 fps variability
DX8
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dx9frames: 112.34 fps 8.330 fps variability
maxframes:115.47 fps 8.673 fps variability
highframes:87.82 fps 6.042 fps variability
default: 83.38 fps 6.941 fps variability
"default" is what the game sets things to with -dxlevel 95/81 still in the launch options
so according to this, for my system, DX9 default performance and DX8 maxframes are identical. what even. also dx9frames gets better performance in dx8, even on my system which seems greatly biased toward dx9? Yeah I have no idea.