Kevin,

I used Canon FTb cameras before 1979, and the FD 100mm f:4 Macro was the lens I used more than any other. When the owner of the shop where I worked in Dallas required that I use an R3 for a week so that I could sell them knowledgeably, I told him that I loved the lenses and camera, but wouldn't change because there was no 100mm macro available for the R system. He showed me a brochure about the new 100mm Macro Elmar-R, and that and the dealer employee discount program (50% of list, or 10% below dealer cost) sealed my fate.

That said, I loved the 100mm FD macro and shot portraits with it, and used it with a lot of Kodachrome 25 before they took all the silver out in 1979. The lens was available with an extension tube that got you to 1:1, and went to 1:2 without it IIRC. I also always wanted the 100mm f:2 (or was it a 2.8? I think they made both and I wanted the f:2.) for available light portraits, but my budget wouldn't allow two 100mm lenses. If you can find that lens and a set of FD extension tubes, it might work well for you. I recall that it performed very well as a portrait lens. A neighbor of mine had one.

The Vivitar 90mm f:2.5 Series 1 macro had a great reputation, although I never used one, so I can't speak from personal experience. You'd be correct about the faster focusing at f:2.5.

The FD 135 f:3.5 I had was also a very fine lens, great contrast and sharpness. Those should be pretty well priced, but the close focus was about 5-6 ft IIRC, and I already had the 100 macro, so I didn't use the 135 for close-ups.

Just to throw more confusion into the mix, and at a hefty price, take a look at the Cosina Voigtlander FD mount Apo-Lanthar Macro 125mm f:2.5, which goes 1:1 with no extension tubes. It's current production, reputedly well-built, and the very few reports and photos I've seen on the net have been very positive. It has good working distance, and is fast for snappy focusing.
http://cameraquest.com/Voigt%20SL.ht...%20APO-Lanthar

Hope this confuses things enough.

Lee