Optically, the Sigma 50/1.4 seems quite good. But when I read reliable reports describing the Sigma's AF as "very inconsistent" (TDP) and "schizophrenic" (lensrentals.com)...well, I'd rather not have my intended subject be part of that creamy bokeh - the best IQ in the world sucks if the lens can't achieve correct focus.
It's interesting that you mentioned the 85L as 'bad ass' - given slow AF, and that the 85/1.8 is one of the best values in the Canon lineup for IQ/cost, and the very nice Sigma 85/1.4 is half the price of the 85L, I'd have thought the 85L would also be an overpriced pile of...whatever.
well, as far as the AF of the Sigma goes.. I had mine calibrated at sigma (took him one afternoon), so did my friend - both lenses worked like a charm afterwords (well up to f/3.2 - never really went smaller) - but yeah, it sucks to be the owner of a new 50/1.4 most of the time.. but in the end.. it pays of.. metaphorically as well as literally..
the 85L was designed with mostly one purpose as far as i can tell.. to get sharp pictures at f/1.2 - does it? yes - and it should.. if you are going to buy that chunk of glass.. you better hell use it at f1.2-f/2.. or you may as well get the f/1.8 you mentioned - the 85L isn´t cheap, but you get for what you payed for, a really "bad-ass" lens you will love to use at f/1.2.. with the 50L you simply don´t get that and if you did.. hell.. charge 2k€ if you will.. people will want to buy a sharp 50/1.2.
as far as the sigma 85mm goes.. sure.. it is half the price, but at least in this case.. you get what you pay for with the Canon.. and that is the only 85mm lens that goes to f/1.2 and is actually sharp when doing so.. and hey.. it´s only 2x the price of the Sigma.. the 50L is 3.5x the price..