I never used my 24 1.4 II all that much below f/2.8 or even f/4 so I actually ended up selling it for the 24-70 II (which, remarkably, more or less matches it for 24mm quality, other than more distortion and bit worse corners near wide open, but with actually LESS purple fringing/LoCA, many shots stopped down were almost identical between the two other than more distortion and LESS LoCA from the zoom; when I compared the 24 1.4 II to 24-105 OTOH, the prime blew that zoom out of the water, yes even at f/8 or f/10, believe it is a fallacy that all lenses perform the same once well stopped down, not even close.) Here and there I miss the 1.4, but not much and love the 24-70 II.
Hmm. I actually shoot the 24/1.4 at f/1.4 on the 5DIII & center AF precision is quite good after AFMA. I do remember corner/side compositions being quite out of focus though at anything wider than f/2.8 or so during the last wedding shoot, so I had to switch to live view AF. Part of this was also just side/corner softness at wide apertures. Actually, it's quite appalling how bad some of these primes are on the sides once you go to a higher resolution sensor -- plop the 24/1.4 or 35/1.4 on a NEX-7 (no optics in between, just a Metabones Smart Adapter) & you'll see flaws of the lens you'd barely see on a 5D II/III or what-have-you FF body with larger pixels. And that's not even using the full image circle of the lens. Use a SpeedBooster to use the full image circle of the lens & some copies of these primes don't sharpen up on the sides until f/8-f/11 (whereas they're sharp by f/4 on my 5DIII). But of course, in the latter scenario I'm adding extra optics in the way... anyway, I'm getting OT now.