Hi Perry,
IMO, when it comes to fast AF lenses, only the 50L beats the Sigma 50 F/1.4 (and any other 50 for that matter). I tested two copies of the Sigma as well, and both were clearly sharper than the EF 50 F/1.4. However, both Sigma specimens did suffer from some focus shift close to MFD, worst at F/2. So, it does look like you need to be rather patient to find a good one, similar as is the case with the 50L.
All other 50 F/1.4s I have tried so far, are all rather soft up to F/2.8, with the exception maybe of the Olympus Zuiko. That is fine around F/2, but it is MF, with adapter of course, and maybe not as sharp as the Sigma at F/2. All 50 F/1.4s except the Sigma, and the 50L, and the Zuiko to a lesser degree, suffer from old lens designs, which may well be a result of the Double Gaussian standard BTW, and that is that they all only begin to shine from F/2.8. This is why I recommend the slightly slower brethren to most people, the F/1.7s to F/2s, which tend to be good to very usable wide open. IOW, the ZUiko, although F/1.4, probably falls into this category (need to do more comparisons to be 100 % sure).
The older Zeiss 50 F/1.4 I have, and this was supposedly a very highly regarded copy, is extremely soft at F/1.4, to a degree that I actually find upsetting. I am afraid that the new ZFs and ZEs are really the same lens design, just in a different jacket and maybe with a slightly better coating. This may result in a slightly better behaviour, but I wouldn't expect miracles. Say F/2.5 instead of F/2.8. Halation at maximum aperture is absolutely awful.
Similar things are true for the new Nikon F/1.4. It behaves, in the tests I have seen, the same as the older ones, be it maybe slightly better again, probably because of improved coatings.
All in all, I did find that the search for an excellent fast 50 was very, very frustrating, just like your search seems to be. And I think there is only one solution for the dilemma this creates. I'd suggest you get a good 50 F/1.8, Mk II, or better a Mk I, and start looking for a good 50L in the mean time. It honestly is the best 50 out there I have seen so far, it has AF, L-build, sharpness, great colour and drool-inducing bokeh, but you just need to be very patient when looking for a good one without the focus problem close to MFD when using large apertures.
However, when you do find one, you won't look back.
Kind regards, Wim