Well I finally got the 174 build downloaded and tried it.
The performance SEEMS better to me, though I'm just running like 1280x800 windowed. With an e8400 and 5850 I usually get 30-40 fps with everything max besides 8xMSAA. I don't use MLAA, FXAA, or HDR at the moment. It sounds like HDR does not improve the look, though there seem to be several HDR modes and I have not experimented with them.
There are still some graphical flickering issues, like billboards or props on some tracks, and the sun looks like an octagon, but things look pretty nice otherwise. The courses seemed reasonably fun to drive, and I just spent a fair bit of time going through different cars and tracks. I'm still not worried about it being too easy, since with the plain new install, I was spinning out in various cars and hitting barriers pretty often. :P
I just saved a bunch of screenshots, unedited and unresized from the ingame graphics, so please excuse any blur or crappy quality. I guess posting the whole batch here would be bad form, so I'll try to cherrypick a few of them: