My 150mm CF is very sharp, right out to the edges, even wide open. I think the 80mm is just fine for most purposes, without bothering with the 100. For shooting handheld, I probably don't realize any sharpness improvement with my 100. One advantage of the 100 over the 80 is that the 100 has no distortion, while the 80 has a little barrel distortion. For architecture, that counts; otherwise, the 80, being the normal focal length for the format, is often better to compose with. I would not be without my 60 CF; yet for some reason, I cannot bear to part with my 60 C T*. For the 50mm, I have owned the 50 CF, and now the 50 CF FLE. The improvement of the FLE over the former version makes it well worth getting the FLE.
I think it is good to select a system of lenses so that they are nicely spaced. 50-80-150. Or 40-60-100-150. With the latter, each lens is 1.5 times the length of the previous one, so the spacing is uniform throughout the set.
The older C lenses are nicely made, with the numbers and letters engraved in, not merely silkscreened on. And I do like the automatic depth of field indicators on the C lenses! The T* coating on the CF and subsequent is better for color. The lower contrast of the C lenses is good for black & white.
The springs for the C lenses are getting scarce. Zeiss no longer supplies them. A time will come when they won't be repairable (unless something happens).