If you have been looking at images taken at f1.2 then I guess it is because the 85 is significantly sharper than the 50 at this aperture:
Clearly the 85 is a much more expensive lens, but the 50 is hardly cheap. I presume on the 85 focal length it was possible to achieve excellent bokeh with more chromatic aberration correction than on a 50 focal length.
There have been a lot of helpful replies to my original question, including Sporgon's link (which I've already thanked him for). This link did plenty to put me off, but Neuro's discussion of the focus shift issue also dissuades me--I was looking for something a little wider than the 85mm 1.2 and with less of a minimum focusing distance.
Right now I can confidently work from three feet to my subject with the 85mm, but, if I'm understanding the focus shift problem, the "real" working distance with the 50mm when using AF is about four feet. While there might be times I used Live View for static subjects, I'd mostly be using this for creative portraits of paying customers and soon-to-be-delivered first child.
Another little twist somebody added to this thread was a mention of the 50mm 1.2 being improved in and after 2010...Does that mean the link referred to in Sporgon's post is now out of date???
The "sub-thread" about changing lenses and gear handling in general is interesting. The photographer I mentioned (she holds one lens between her knees when swapping out) is among the higher end (price-wise) photographers in the southeastern US. She takes good care of her gear, but when she is working a wedding or commercial project, she is focused 100% on getting the job done superbly. (I believe she began her career as an army photographer in the Middle-East.) She does keep a second camera close by (usually held by her assistant), but she happens to be only 5' tall, and her style involves a lot of kneeling down and even laying on her belly or back, so having two cameras around her neck just wouldn't work.
I read some time ago in a Moose Peterson blog about metal particles being a component of sensor dust, and he recommends wiping the lens and body mount rings fairly often to reduce the amount of particles which get intot the camera.
As for myself, many fellow photographers laugh at me because I have to put my camera down and the lens I want to put on it down to change. I've simply never developed the confidence to swap lenses regularly while standing, though having a vest pocket does make it possible for me. I try to always keep the body facing down to reduce dust falling in (though I know dust swirls up a lot too); and I try to switch very fast.
I've lost shots at times because I was too worried about switching to the appropriate lens during the extreme pollen times we have in our area--especially on windy days.
In a way, this discussion of changing lenses is pertinent, because many of us seem to agree that both the 50mm and the 85mm are lenses for specific shots, not for the majority of work at an event. Having the confidence and competence to swap out quickly when needed is, in my opinion, one of the basic requirements of a topnotch photographer. Otherwise, why use a DSLR? I wish I could get faster and not be so worried about dust.
Very good points, and well stated too, thank you. However, in my opinion, or at least for me...it's not an issue of "confidence". It's an issue of "consciousness". But I agree, if I was making $8k a week shooting weddings (during the wedding season), I would not give a second thought to switching lenses quickly, or doing whatever I needed to do, to get the job done. (I don't know if I could hold something between my knees, due to my anatomy, but I'm willing to try it sometime...haha. My thighs are not small, and it's not fat.) Unfortunately I do not make enough money from my photography, to take such an approach with my gear. Nor do I want to need to. And about pollen...well, that can get inside your lens, even if you don't take it off the camera (and even if it is weather sealed). I don't have the "confidence" to rip my lenses down and wipe the internal dust out on a regular basis, though I'm sure some on here not only do it regularly, but have done it hundreds of thousands of times, etc.
Also agree with the point about the metal fragments...but I suppose since the mount has a spring, that makes everything fine, there's no metal fragments. I can sleep better now.
If the reason to own an SLR, is to change lenses as much as possible...that's a race I don't feel the need to compete in. I change lenses when I need to, and try to avoid doing it outdoors. I am a neat freak that way. Others aren't, and that's fine. I don't miss shots too often doing this. Obviously it depends on how often you need a different lens. Again I would own more than one body, and work around that.