Do u mean there nice new 90Nm core? NV80 seems to bring up reslts on the 4400Ti, which i have a feeling isnt what u mean!
I dont think nVidia has released much about it yet, i would have thought they would wait until the announcment of the x1900 and work from there!
Ive not read anything about the new core apart from, its coming.
Thing is 2 7800GT's are still going to have more than enough power run anything smooth and looking fine. I would have thought the new core will replace the 512 as the king of the nVidia range. Then slowly filter it down.
This is however a guess.
Could be worth waiting a bit and see what happens, worse case is that things get cheaper so you could get GTX's instead!
BS