So far, the preliminary dx10 benches (admittedly for one thing or the other only, not a cumumlative test) show the r6xx core to be about 5 times faster, give or take a few magnitudes.
Don't judge the performance solely on dx9 (which is more than fast enough) but also by dx10 (where the extra shaders seem to be doing an pretty decent job).
Besides, there are some ace features, such as the dvi/hdmi thingamejigger which is quite excellent. This is a PACKAGE and if I can get my hands on one of these buggers for about $350 or so (once a folding client is out) I'll be all over it