I have the 1.8 85mm and use it a lot, and saved a bit on going to it rather than the older 1.4, and don't thing I'll move to the newer 1.4 either, just as a matter of economy.
The extra 2/3rds stop can be meaningful to all at some time, but I've managed with the f1.8 well enough. I like the lens. If one has the extra cash to spend, the faster lens will be clearer to see in low light for sure.
As a practical matter, however, I don't know if one will actually shoot that much at f1.4. One will typically punch up the f-stop a bit to increase the DOF a smidgen to ensure more sharpness over facial features in portraits for sure, even if it's just f3.5 up to 5.6, negating the additional gain in the fast lens. I really doubt I've missed a single shot for lack of the f1.4 setting.