Dan Brown , Mar 17, 2000; 10:14 p.m.
Let me start by saying that I have not tested, or used either lens.
But, I did speak at some length with a tech. rep. at Kyocera about Contax/Zeiss lenses and I have read most of the material on the subject of these lenses.
The new 28-70 was designed for the Aria. It uses a simpler optical design and takes advantage of the lighter weight and lower cost of plastic. This resulted in a lens that was cheaper, lighter and smaller than other Zeis zooms, such as the 28-85 you mention.
The net affect of this is that the 28-70 seems to be competitive with other brands of lenses designed in a similar vein. That is, the 28-70 appears to be a medium quality lens, especially in terms of performance.
My reaction to all this was to avoid the 28-70 in favor of primes. this is not to say that other Zeiss zooms aren't excellent. I have reason to believe that the 100-300, for example, is an outstanding lens that compares favorable with primes (Zeiss primes) and that ain't bad.