Just in case anyone is interested I went ahead and bought a fringes ef/fx pro2. It cost me $450 au new and also picked up a 150 - 600 Sigma contemporary for $814 au used in top nick... wow...! Very happy with the results.. to be honest the autofocus works great, not as fast my 55 to 200 but not that much slower either, very usable. The Sigma is on the heavy side but 600mm mmm mmm love it. I can still hand hold. I had a bit of a play around the house over the last couple of days and have so far enjoyed using it and haven't found any real faults. I've used a canon 70 to 200mm L ll f2.8 and once again the autofocus was a little slower but not by much. I'm not a professional, I'm just letting people know that the fringes works and works well.. so if have some Canon lenses or I would like to get a cheaper option then the fuji 100-400mm and 1.4 extender is all. I do not regret my purchases and I am now looking at Canon lens options second hand like the 300mm prime. Hope this is of some help