A question about Contax Zeiss 85mm f 1.4 lens

[milandirector]

Hi,

I managed to find Contaz Zeiss 85mm f1.4 lens for about 700$ (in decent condition) and I also got Jupiter 9 85mm f2. Is it a huge difference between these two lenses, and should I go on to buy the Contax lens, already having Jupiter one?
Another question is about mount adapter for this lens and GH2 camera. It says that it's "AE mount for RTS camera bodies", so do I get Contax Y mount adapter as is suggested in Andrew's GH2 shooter's guide, and do you have suggestions for the good one?
Thank you very much for your responses...