Will the NV30 annihilate the 9700 when it comes out? No, of course not....
Will the NV30 outperform the 9700 by a measurable amount? We don't know for sure but I would assume so. Especially after the drivers are optimized...NVIDIA is famous for getting every last bit of performance out of their chipsets. If the NV30 has as much headroom for overclocking as the 9700, ATI could be in trouble until their .13 part makes it to market.
Consider this fictional scenario ( nobody knows for certain ):
NV30 is faster than 9700 : ATI raises core frequencies and memory freuqencies ( maybe even introduce DDR-II ). At this point, they are out of any major options. The design is "maxed".
now 9700 is as fast or faster than NV30 : NVIDIA raises core frequencies ( yields will get better to allow this ) and memory frequencies. At this point, NV30 could still have some headroom as it has a smaller ( more efficient ) die-size and is using DDR-II.
Back and forth until one card runs out of options...Because NV30 is using slightly newer technology, I would assume that the 9700 would run-out of options first.
As far as the .13 vs. .15 comparison speed-wise, I think we can all safely assume that this would hold-true. There are so many benefits to the smaller die size which would definitely be taken advantage of by expert companies such as ATI or NVIDIA.