I own, have used, and consider both the 50 1.2L and the 50 1.4 great lenses. From my real world experience, the L has better bokeh, color/contrast at all apertures, and better build quality. The auto focus accuracy/consistency of the L is much better than the non-L wider than f2.8 (as good as my other L primes), and they are about the same smaller than f2.8. The non-L focuses insignificantly faster in good light. The L’s low light auto focusing ability is extraordinary. Better than any of my other fast L primes. It will literally snap into focus in a dark room where other lenses just hunt and fail. It’s downright difficult to make the L flare. Both lenses are sharp. The L is slightly but noticeably sharper wider than f2, somewhere between f2 and f2.8 they become the same, and I can’t see a difference smaller than f2.8.
If you frequently shoot wider than f2 or in low light situations, then the L is well worth the extra money. If most of your shots are smaller than f2.8, it isn’t. If you shoot mostly in between or at a wide range of apertures, then let your wallet be your guide.
Good Luck with your decision.