I bought the 100mm f2.0 Zuiko new in 1987. I can't say about the 100mm f2.8 as I have never used one. The 100mm f2 was my first good telephoto. I also own the 85mm f2 Zuiko and I can see a noticeable improvement with the 100mm f2. If I am looking at a photo from the 100mm f2 and one from the 85mm f2, I can always tell which is which. The 100mm f2 has a special way of rendering on film that no other OM Zuiko has. Bokeh? I know that this lens has has a unique way of rendering that I cannot get with any other lens.
As for the 40mm f2 Zuiko, I have one but I prefer my 50mm f1.4.