The Zeiss 135/2.8 lens for Contax is very good - but at this focal lenght and f-stop many lenses are at least good. The Zeiss Planar 135mm f/2.0 is expensive - but I read good things about its IQ.
The 85mm f/2.8 seems to be stellar, but slow. The f/1.4 version is regarded as a very good portrait lens, but not exeptionely sharp. There are sharper lenses around.
My own experience is that the sharpness is good enough for my DSLR when the lens is at f/2.8. It is optimized for longer working distances, this is sometimes a drawback. The AE version of the lens has jigsaw bokeh when iris is closed to some f-stops ~2, 2.8, probably 4.0. With MM this is no problem.
I love the bokeh of this lens - no onion rings.
The Zeiss 85mm/1.2 is expensive - not sure about its quality in comparison to the Canon 85/1.2L EF and FD lenses.
The Zeiss Contax 300/4 is big, and its focussing is a normal helicoid, no IF. Because this the lens is much slower to focus (in comparisson to Canon FD 300/2.8L).
I heard the lens has CA problems on DSLR - but at the moment I have no experience regarding this. Used it not often.
Don´t know much about the Zeiss Contax 180/2.8.
Longer fast Zeiss Contax lenses like the 200/2.0 and 300/2.8 are very expensive and rare.
But even the cheap Tokina 200mm f/3.5 lens seems to be a good performer - the same lens is sold under different names.
What is "fast" for you?