One thing for sure that 50 f1.4 can't do is shoot at f1.2
The 50L will shine if you shoot at wide open. I like mine @ f1.2 to f1.6ish. As an owner of 50 f1.4 & 50L, the L has much better contrast, color and bokeh.
Sharpness is excellent @ f1.6ish - my copy of course.
Funny... I was thinking of you when I said that SOME PEOPLE say it is really good.
My rule is quite simple. I don't give comment or advice on camera lenses or bodies that I haven't touch. How often do you see that happen here on CR. Below are couple shots I took with 50L at f1.6(straight out from camera) at Pretend City, in Irvine, CA. For those been there would know the light condition is not that great.
Off topic: I think you should get 85L II for new born.