Eh, the earlier C-style 50mm Distagons had used Series 63 filters. They are not bayonet filters but are set inside a special filter ring or the hood. The same filter size was also used with the SWC cameras until they also standardized on the Bay60 filters.
Second, in general chrome C lenses doesn't have multicoating, i.e. T*, while the black C lenses does have T* coating. (There are exceptions, but they are very few, read "expensive" as in collectors items.)
What is more important than optical performance when it comes to choosing in between a C lens and a CF lens is that spare parts for the shutters on the older C lenses are running out.
If you buy an older C lens it is important to first check that all the times are correct and then to excersise the shutters every month. (E.g.: Today is the 25'th so it's shutter excersise day. Oh yeah, it's payday too.

(In Sweden paycheck days are normally once a month, on the 25'th.) )
//Björn