If I were you I'd buy a 50 1.8 and see how often you actually use it.
I had the 50 f/1.8 when I only had an 18-55mm and a 75-300 (and eventually the 55-250mm). But the lens is soft from f/1.8 and sharpens up around f/2.8... which is where I mostly shot with it. I eventually upgraded to a canon 50mm f/1.4, but at that time I had a 24-105mm and I think a 100L... so by comparison, the 50 wasn't really that good. Not enough reach (on my crop 60D), and not wide enough to use indoors. So even though the f/1.4 is an overall better lens, it was my least used.
It's a fine lens. So is the 85 1.8.
I had the 85 f/1.8 and I liked it. I took a bunch of photos of my new born... but the minimum focusing distance (and I realize the 85L mkii also has a mfd of 3ft) was annoying... and I sold my 100L after getting the 70-200mm f/2.8L mkii, thinking it was redundant... it wasn't. I missed the 100L's MFD and just dramatic sharpness... So I sold the 85 f/1.8 and I bought the 100L again.
The 85 1.2 is good in a studio on a tripod. It's harder to use in the fly. At 1.2 there isn't much forgiveness in depth of field and you need an ND filter in sunlight.
I was using a depth of field calculator and the 100L @ 12 inches away has a SIGNIFICANTLY thinner depth of field than the 85L at f/1.2 and 36 inches away. It can be a challenge working at thin dof's... but not impossible... and if I can get a decent amount of hits with the 100L... the 85L doesn't scare me...
The 40 2.8 Is an option I don't use it enough but is also quite a nice lens.
I bought one for my daughter... she doesn't use the camera or the lens... but it's an option there. F2.8 is fine... but I do want something with a wide aperture for situations like last night... we were at an amusement park and it was dark save for the lights off the rides and lamp posts... but I wanted a wider aperture to increase shutter speed/lower the iso... Funny thing... that's why I got the 85mm, for campfires and the like... but evidently I forgot that I need a wider aperture lens when I sold it.
I can see you are going for quality over quantity on you lenses which is quite sensible.
With your buying pattern I'd say the Sigma art is the best choice for you.
I want the 50 art... and I'm willing to only use the center AF point and only use manual focus... I was comparing the 50 art to the 55 otus (test charts) and the otus is impressive from center to corner, but I can be content just having a really good performance and great performance compared to the rest of the 50's.