I have 60B and I played with it some and the filter affected focus. I always use hood too. been a while, seems I didn't test sharpness and ca but since the focus seemed right with the filter installed that way that's how I used it. Maybe I'll have to test again. My tamron 2x is absolutely awful with this lens, have to use at f/11 or 16 (5.6 or 8 on lens) where there is a huge focus shift. Have gotten one really really good photo with this combo probably due to decreased contrast, and resolution was adequate.
Sometimes mine has a bit of the glow that some older lenses have wide open, but then sometimes seems ok. Perhaps you have a better copy? I definitely use mine wide open when I need it.
200-500 31a is pretty good. Mine seemed a bit sharper than 100-400 L that I used! Kind of wonder about that opinion but that is what I remember. very big and heavy, not really handholdable like 100-400, and a pain to use, but pretty good. Better stopped down a half stop or more, I use it at f/8 1/2 a lot. Weight listed on adaptall-2.org is 6 lbs. so maybe about the same as canon 300/2.8. Used it with tamron af 1.4 tc and got ok results, need to tape contacts or something to get it to work, though. I recommend the 200-500 31a, definitely worth a look. Usable wide open, better a half stop down.