I've not seen any comparisons of these two lenses but the mtfs are amazingly similar.
The 16:35 is here:
and the 17-35 can be downloaded as a pdf here:
I have the 16-35 but I think I'd be happier with a 21 distagon. May switch at some point.
I wonder in view of the 24-85 Contax N lens why Zeiss and Sony decided on the narrower range of the 24-70. From what I've read and from looking at the mtfs of the 24-85 it does look like a nice lens. I suppose the reason may have been that f2.8 constant aperture was more important than the wider range.