If we look at the following page:
http://www.tomshardware.com/2007/12/12/geforce_8800_gts_512_mb/page2.html
You can see really the only areas the 8800GTX have over the 8800GTS 512 is the memory bus width (256 vs 384bits) and the ROPS (16 vs 24).
Now I know everyone has their theories about the memory bus width and obviously this won't change. BUT I think one key items is the number of Renduring Operators. These get clocked with the GPU and are in fact part of the GPU. I mean My 8800GTS is clocked to 750MHz right now without a sweat. Which if the 9800GTX is at 675, well SUCKS. My thought is they are going to pack more ROPS into this thing making each clock cycle more "powerful" in a sense. This, I think, is why we see such a better result overclocking the GTX than OCing a 8800GTS512.
Just my thoughts. So if they come through with more ROPS for the new GTX it might actually be a good deal. STILL, granted I was looking for something that would knock my socks off but I don't think Nvidia would let an overclocked GTS outperform the new grand daddy GTX.