08-09-2016, 08:29 PM
Might be too late to join the discussion already, but I guess I can share my story. As for portrait lenses, I'm really a fan of the fast glass even if I don't use it at f1.2 or 1.4 all that often. I tried different lenses starting from the "reasonable" 1.8 primes, then eventually going for the pro f2.8 zooms, some macro 100mm in between, then migrating finally to fast primes ...and selling the other lenses to finance it 
A rather expensive way to find out what I really like, granted, but it's just that with the fast lenses, usually at the top of the ladder, I found better drawing, colour, contrast. The wider aperture, wide-open bokeh and limited DOF was a bonus.
However, that is a subjective choice and yours might be different. It's not always a rule that a (new ) fast lens has to be better than the old - it all depends on your needs. For me the Canon 85L 1.2 is so much better then either the f1.8 or the macro 100L (slow AF), that I had to take the plunge
Back in my Nikon days I enjoyed a lot the 85mm 1.4D, a much nicer rendition at wide open till f4 then the newer 85 1.4G lens - but that is my own preference, for a classic look where the "center" is reasonably sharp and the outer part of the frame goes away in a nice blur Then maybe that's also why I'm so tempted to try the Fuji X, despite it's limitations, but drawn into it becouse of the colour and overall rendering of the image with the Fuji primes (35mm and 56mm). Well just my 2c
A rather expensive way to find out what I really like, granted, but it's just that with the fast lenses, usually at the top of the ladder, I found better drawing, colour, contrast. The wider aperture, wide-open bokeh and limited DOF was a bonus.However, that is a subjective choice and yours might be different. It's not always a rule that a (new ) fast lens has to be better than the old - it all depends on your needs. For me the Canon 85L 1.2 is so much better then either the f1.8 or the macro 100L (slow AF), that I had to take the plunge
Back in my Nikon days I enjoyed a lot the 85mm 1.4D, a much nicer rendition at wide open till f4 then the newer 85 1.4G lens - but that is my own preference, for a classic look where the "center" is reasonably sharp and the outer part of the frame goes away in a nice blur
Then maybe that's also why I'm so tempted to try the Fuji X, despite it's limitations, but drawn into it becouse of the colour and overall rendering of the image with the Fuji primes (35mm and 56mm). Well just my 2c