When I went to medium format with a Rolleicord, a Bronica and an RB67 I kept my 35mm cameras as something small to carry around. However, my 35mm cameras are a Nikon FG and a Nikon F601, both of which are compact.
The F6 is a large camera and therefore, I see no advantage in using it over the Contax as they are of similar bulk.
However, if I had an F6 I don't think I would get rid of it!
(That doesn't really help much does it?).