Whilst I have, for my Contax G2, my svelte Sonnar 90mm f2.8 for my Zeiss Ikon I have my Sonnar 85mm f2 ZM. It's monster.
Zeiss described the 85mm f2 Sonnar as "the first M-mount tele lens with floating elements, containing Carl Zeiss cine lens technology". The lens was made in Germany rather than Japan as it required more precise engineering as it was complex to construct, perhaps too complex for which read too expensive as it did not stay in production long. But it was a real goodie, big but good - materially, mechanically, and optically as we shall see.
The comparative size and weight of this f2 lens is a monster, though on my camera it feels better and more balanced than on its own. It uses internal focusing which greatly helps the handling of such a lump of a lens on camera. It has an unusual tapered shape intended, I guess, to reduce its intrusion into the viewfinder frame to aid composition. It is a beautifully made lens and smooth to operate.
Optically it is typically Zeiss i.e. lovely - with rich gradation, clear, three-dimensional reproduction along with high colour saturation. One thing to watch out for is the need to be precise and careful when focusing the lens when wide open as it has, as you would expect, a very shallow zone of focus at open aperture and it is easy to "miss" with hurried or sloppy focusing technique, particularly at closer distances.
Having such a wide EBL on my Zeiss Ikon rangefinder cameras helps with accurate focusing in this regard but common techniques such as focusing on one object in a scene then recomposing by swinging the camera with this lens used close up and wide open at f2 for example often disappoints!
Thus I have my Sonnar 85mm f2 ZM for my Zeiss Ikon which is monster - a rare but lovely optic by any standards.
Now imagine this lens at f2 using Kodak Portra 800 pushed to 3200, yeah - my available light monster!