Marc, I'll give you a slightly different perspective based on my two years with the Contax 645 system, during which I used every Contax lens except the zoom.
The Contax 120mm is a gold-standard lens that stands comparison against any other optic I've ever used. I wish the Hasselblad V 120mm macro was as good. The 140mm on the other hand is okay, but IMO will never take a seat in the pantheon of world beating lenses.
However, if you want an objective measurement rather than a string of opinions then print out the MTF charts for the Contax 645 lenses versus some Hasselblad V alternatives from here,http://www.zeiss.de/c12567a8003b58b9/Conte...12570f90049667d
And also get the Hasselblad H MTF charts from herehttp://www.hasselblad.co.uk/products/h-system/lenses.aspx
You shouldn't normally compare MTF charts from different suppliers, however the Hasselblad MTF charts are made using the same Zeiss testing equipment that Zeiss themselves use, and to the same operating procedures. What you'll see is what I experienced, the Contax 120mm macro is outstanding. The rest of the Contax line-up gets trumped by individual optics such as the 38mm Biogon, the Hasselblad V system 40mm IF, the Hasselblad H system 80mm, the Hasselblad V system 100mm, the Hasselblad V system 180mm, the Hasselblad H system 210mm, the Hasselblad V system 350mm tele-superachromat etc.
Don't get me wrong, Contax lenses have specific virtues of their own, mellifluous out of focus transitions for example, and they're certainly no worse than venerable Hasselblad warhorses like the V system 150mm. But if for you it's all about absolute resolution then IMO you'll do better elsewhere.