I made a choice and since members have been kind enough to post some advises, I believe it is my duty to contribute in articulating my review of the lens (and choice).
I ended up buying the Canon 100L and not the Sigma 150mm.
+ Sharpness: excellent
+ Color and dynamic range: very good (though the tint seems to be a bit on the pink side, easily fixable in post-p)
+ Very versatile: great portrait lens (love the 100mm length / compression on a FF), interesting length for landscape photos (although I wished several times I had a zoom)
- Bokeh = barely decent. I wish it could provide the Bokeh quality of the Canon 50 1.4
- A bit short on a FF for tiny insect macro. By the way, to remedy this, could someone tell me what would be better a (series of) Tube(s) or an Extender x1.4 or x2 ?
- Autofocus seems a bit slow. But maybe I have a bad copy. And lately I have noticed I have an unsual low rate of keeper. Focus misses the mark - nothing is in sharp focus not only at 2.8 but even till 7.1 (and it's not shutter speed issue, neither an IS turned on issue). Not sure if it is an AFMA issue or if my 5D3 has a problem. My 5D3 does its job in terms of AF with the 17-40 but it was impossible to get more than a 2/10 keeper rate with the 50 1.4 that I ended up selling (same problem - nothing in focus).
I read some people ship their body + lens to canon to make sure everything is okay. Is this free of charge?
Thanks for reading.