Well I don't know, I had the 35 Art and it's the best price/quality 35mm, but sold it as the 24-70L is more useful for the 24mm.
But I like primes so I bought the 50 Art, sharper than the 50L and the best 50mm up to date.
I have the 85 1.2L, just did a shoot with it last weekend at f1.2 (narrow dof yes, but for frontshots or fullbody at further distance it's the best), I don't see the need to go for the 85 Art.
With the other Sigma 85 the bokeh was less nice if I remember good, and f1.2 is still a tad faster and legendary
About the 12-24 f4 Art, it's an f4... just like my Canon 16-35 f4L IS that I sold recently.
I sold it to buy the Venus Optics 12 2.8 Zero Distortion prime, this lens is more wow that the Sigma.
Although i'm a big Sigma Art fan, I'm still considering each brand according to the quality, how tempting the Art's may feel
But this time Sigma misses an important factor of their previous successes against the competitors : price point...