IIRC, GF6800GTX < X800XT PE, but GF6800GT > X800XT. Problem was that the PE was nowhere to be found for months, so for all practical purposes GF6800GTX was the sole performance leader for most of the generation. Also, the 6800GT was only a clockspeed downgrade, and it went against the X800XT which had reduced pipes. That means the big mover of the product lines went resoundingly towards the GF6 line. Plus the NV40 had SLI and SM3.0, something the R420 line didn't have.
That is the impression I have of that era too, and why I got a 6800GT back then.
This was a very surprising recovery from Nvidia. I find hard to believe that a company can simply pull a rabbit of its hat when asked. ATI probably does not a have a miracle product waiting in the wings to save them in 2008.
Yup, they took me by surpise too, but then agin, back then they also employed the same false PR to mislead people into thinking that the 6800 where "less" than what they showed to be, just like with the unified pipeline in the G80...
They have been real sneakey at doing stuff like that...