I think the yield problems of GT200 chips should mostly be due to its massive size, not the problems with the chip itself.

And if you're right and we don't see an 55nm GT200 until near the end of the year, NVidia is really doomed for the time inbetween. I don't see them lowering GT200 prices even more. GTX 260 was already dropped from $500 to $400 anyway, and another $100 drop to make it actually competitive with 4870 is unlikely. And GTX 280 definitely needs to be dropped to around at most $450 if 4870x2 is to be released at $500. ATM NVidia can only compete at the $100-$160 price point.

ATI will sell billions of 4800's by that time; and by next year's January they will have announced the RV800's.