The 9800GX2 is not a midrange card at all. It's top of the line!
Wikipedia says 30-50% faster than the 8800Ultra.
HardOCP says at least 30% faster.
It will support quad SLI, so if you wanna get 2 of these bad boys then you'll have pretty much the fastest gaming setup available.
What I want to know is the price of the 9600GT with benchmarks. If this card is only $450, the 9600GT has to be significantly less.
Post a new thread when the 9 series has been released (rumored mid February) and we can make a complete list of things then. The X48 chipset will probably be more available then also.