No direct comparison, but I owned the ZM 35/2 for the better part of 3 or 4 years and the KM 35/2 about a half a year. The ZM 35/2 is clean and really sharp wide open with gentle transitions from in-focus to out of focus areas.
The KM 35/2 is similar to the 35 ASPH lux in terms of rendering. The out of focus areas are a little bit more harsh, the center is bitingly sharp and the corners fall off, when the lens is wide open.
That said, the ZM 35/2 has third stop aperture clicks and a dinky focus tab. I sold it, and purchased a KM 35/2 instead, mostly for ergonomics.
Either lens is great.