I've used the Sigma Ex Dg 85mm f1.4. Its a great lens, razor sharp with great isolation, compares very well with the FA 85mm. I sold mine because it was too specialized and I hardly used it. Like its smaller brother the Ex Dg 50mm f1.4 HSM it renders on the cooler side. I personally don't like the way the Ex line renders (I prefer the Pentax-F 50mm f1.4, and your FA 43 and DA* should be even better) As far as character goes, the DA* and the Fa 43 would please you more. The new art series coating is much better (I have the Art 18-35mm f1.8 and like its colors) Sigma is going to update the 85mm f1.4 prime, there's no news if they'll come out in K mount yet. I assume the new one will be superior to the old one but since the 50mm Art is almost a grand, the 85mm it's going to be even more expensive.
I would strongly encourage you to look into a older -F/FA 135mm f2.8 lens (I have the -F series and I love it to bits, they're incredibly sharp, have great colors and amazing bokeh (since I don't believe you own a fast 70-200 zoom, but I might be wrong)
Pentax-F 135mm f2.8 @f7.1 on K-5iis
crop: