3rd party 300mm with converter for G3

Hi, everybody. I have always been interested in the micro 4/3 "G" bodies. They are so lght weight and it seems that they take great photos. I am thinking of investing in a G3 for our video/photo company. I have a Nikon 300mm f/4. I would like to set up a G3 system for bird photography and was wondering if aybody uses Nikon auto-focus lenses with adapters with panny "G" bodies. Another option would be to sell the Nikon (it is new) and with the money buy a cheaper Contax 300mm f/4. Any tetimonials of your experiences with either of these two lenses on a "G" body would be greatly appreciated. I like to get the best quality possible. Thanks to all.