In a completely unrelated note, coming from another source, the R420 is a 12x1. The NV40 is still a 8 pipelines design AFAIK.
From Notforidiots
They say the reliability is "very high"
Also:
According to Hellbinder on the nV News forums ( paraphrasing ) :
The R420 chip ( *not* board, this is not multichip ) is made out of RV350 ( or RV360, but they're the same thing really ) elements thanks to physical reuse, giving the ( theorical, at least ) power of 4 RV350s ( at Radeon 9600 Pro speeds ).
Such a move makes perfect sense considering the RV350 is currently ATI's only 0.13u chip and that they recently announced they'll use physical reuse for future products.
NVNews news on it
And from NVnews forum about it
(posted in Video forum too, because some people don't check both)