Sigma 85 is a very sharp lens but purple fringing was something that I couldn't live with too. However, CAs are always visible at wide open doesn't matter which lens you use, more so if you shoot at 1.4 in middle of the day on a bright sunny day. But CAs can be an easy fix in PP but they never completely go away in some of my images taken by this lens and that is one of the reasons why I sold mine. The other reason is its weight which matters if you have to lug around all day with it. I got an Nikon 85 f1.8, it's lighter and very, very sharp @ 1.8 and never felt the need to go back to 1.4. Unless you compare each image side by side, you simply can not tell if an image was taken at 1.4 or 1.8, well I couldn't anyway . For Nikon users, It's only a 2/3 stop, if you need an 85mm, test drive the 1.8 first before getting a mortgage for the 1.4 IMHO.
Cheers
Dean