Yes, I have compared Vista DX10 to Vista DX9. Actually, in
here I posted some shots of PCSX2 (svn327, gsdx 0.18). I see virtually no difference in Vista DX10 vs Vista DX9.
And of course, Vista Aero is running, just like XP Energy Blue is running. Throwing the XP shot aside, you can see that DX10 yields only a 5fps increase.
That's it for now, since I don't think comparisons with games like Crysis as benchmarks will be satisfactory. In this case, DX10 is really utilized for better emulation, and it doesn't yield such a performance boost. Enough said.
I'm still dual-booting, and I still love Vista for the ease of multitasking, and to be quite honest, the OS flies on my rig. But that still doesn't mean it's not a bad one.