Thank you for the comments. Again, the 1.2L is a great lens, but I don't know if its a great lens for me. It seems its virtues start at F/1.2 and end around F/2.8. Art is not solely relegated to narrow DOF '3D-like' shots -- how do I catch a candid of three people in a poorly lit room at F/1.2? There is no working DOF @ F/1.2. If they are lined up on a wall, I've got a shot, but that rarely has been my experience.
To be fair, I've shot a lot of L primes and this isn't one of them. I owe it to myself to rent both lenses (when available) and compare them in my shooting environments. That's likely to happen.
As for the engineer lightening up, it isn't going to happen. I do try, but I'm wired this way.
Sure completely understand your engineer pov.. (studied Mech Eng then switched to a photography degree
) So trying to help solve your situation needs, I think maybe the 50mm view might not be the best or only lens needed.
If you are indoors shooting candids then 50mm may be too long and as you say have too narrow DOF at wider apertures. How about a 35 mm, either the new IS one or the Sigma? As shooting at even F2 you'll get a lot more DOF than a 50mm and I'd say you might get a more fun engaged feel as you can get closer to your subjects and easily get 3 people in the frame. Plus it may be better for landscapes and general outdoors / city roaming shots as well.
Then continue to use the 50 1.4 for more tighter in portrait type shots, and if you want to shoot some gigs then maybe a 100mm or 85mm USMs could be good for that and get you a bit closer while still having a wide aperture to help with low light.
50mm is a lovely view but sometimes I find it too close for indoor situations. If i use it indoors in informal occasions I tend to only get one person at a time on the shots (plus more of a head shot or chest up view) and like you mentioned a very limited DOF .
Or even a 24-70 2.8 could be the one for you unless you are driven to primes which is not a bad place to be!