Typical thread on the 24-70 where all the owners will come in to support this lens regardless of it's limitations. I've personally shot with the 24-70 and while versatile, the rendering of subjects (bokeh quality included) and capability to shoot in low light is nowhere near any of the primes in this range.
A lot of people 'claim' the 24-70 can replace primes in this focal length, but I've found this couldn't be further from the truth unless you absolutely hate shallow DOF shots.
Bottom line, I recommend reviewing the lens sample forums on this site and view photos from each thread (24-70 & 85L 1.2). See which lens better matches your shooting style. I typically review the 24-70 thread each week (out of curiosity) and I must say, it's usually one of the more boring threads from an 'excellent/amazing' photo perspective. The prime threads on the other hand usually blow me away with the quality of bokeh, limited DOF, and technical capability of the photographer. You'll never be able to reproduce photos like that with a basic 24-70 zoom, even if it is rather fast at f2.8.