I have neither the FA3m nor FA77mm , but the FA31mm and a few more primes. First let me say that I fully endorse your decision to go for a FA Ltd. They are great lenses IMHO and the FA31mm Ltd is brilliant.
If you want to shoot sports and portraits, I would recommend the FA77mm Ltd. I think that it complement your own lenses and the focal length may be more useful.
I shoot sports (VB, swimming) including being able to get close (next to sidelines). I have used a range of primes incl.a 58mm, a 85mm, a 90 mm and a 125mm. I would say that 58mm is to wide and 85mm is usually the best choice for me. This leads me to my suggestion for the FA77mm.
I hope that the comment may help.