Cool lens collection, Duncan!
Yes, the f/4 max aperture made me avoid the FD 17mm f/4 for decades. I often used the 20mm f/2.8 hand held indoors at 800 EI where an extra stop down would have made the 17mm less useful.
But then I bought the 17-40mm f/4L in EF mount so go figure; I don't use it indoors handheld obviously though with 3200 EI it would probably work. The lens is a bit squishy in the corners until you stop it down a lot, vignetting too but I still like it and use it a lot on my EOS cameras. Great color and contrast and very sharp if stopped down.
I have a Peleng 8mm f/3.5 circular fisheye which I can use on FD or EF mount. It is fun but I don't use it much.