There really isn't much out about either of ATI or Nvidia's DX10 offerings.
Nvidia is supposed to release theirs Q3 of this year. ATi is aiming for the end of this year. As for the price, I wouldn't know. I would guess they'll be more than the current mainstream cards, but the current mainstream cards will probably drop in price before then. We'll just have to see.
Well, if it was me, I would wait. You have a good enough system to get you through till they're released.
Some info I found on Wikipedia. (None of this is official, I don't think.):
Nvidia (G80): 48 Shaders; GDDR4 memory, but the flagship card may have XDR DDR; built on 80 nanometer technology.
ATI (R600): up to 64 shaders; GDDR4 memory; similar design as the XBOX 360 video card (ATI built that, so that's why.); built on 65 nanometer technology.
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