Thanks for the comparison.
From what I read in many forums, Sigma performs best in terms of AF performance, i.e. AF (i) speed; (ii) accuracy; and (iii) repeatability.
With taking into account the caveat you mention in your Sigma review, which lens' AF would perform better, say, in a condition where my kid runs towards my camera 10 meters away or vice versa or she plays with the dog within 10 meters range (running from left to right, move towards and away from the camera) while there are also other subjects and (mostly stable, but sometimes moving) people within the frame? In such conditions which lens can more fastly and accuretely focus and re-focus, and if needed, continuously focus better?
I am torn between Nikon 85mm 1.8G and Sigma 85mm 1.4, and AF performance will probably determine my decision. Even though I know there are much better lenses such as 70-200 VRII in terms of AF, 1) I don't own that lens; 2) I may never own it for monetary purposes; 3) even if I own it at 85mm these primes would better isolate my subject. As a matter of fact, I am not looking for an 85mm prime alternative, even if such alternative's AF may perform better. However, if you say that none of the 85mm primes you have reviewed can do the job in the above-mentioned scenerios, then I may seriously consider an alternative.
PS. I will really appreciate if you can evaluate my question from two perspectives where, with regard to Sigma 85mm, in the first one, I would "let the lens pre-focus to get in the right ballpark regarding focus-distance and then focus a second time to nail the shot" as you mention in your review; and in the second one, I would not deal with such an hassle-- by the way, even if I am willing to deal with that hassle and really get accustomed to it, does not that inherently affect AF performance, especially speed?