Yes, I am aware of IBM being the FAB house. Rumors are saying that the NV40 is SOI, but I have not been able to confirm that.
The amount of power they need and the cooling would seem to indicate it is not SOI based.
NV40 is a much better product then NV3x ever was. NVidia will be glad to drop those products due to all the hardware/yeild problems with them.
Performance wise, it should be close. I think NVidia will win in some areas and ATI others, as far as raw performance goes. It really depends on the ram speeds ATI goes with.
With what is known, ATI will maintain its edge in AA quality over NVidia, and in lower power consumption (less heat).
Other than that, it is a grab bag right now.