My findings are very different from the DXOM results, It could be that their 1.8g sample is a lemon, or that my 1.4g samples were both bad. In either case, what put me off from keeping the 1.4g mainly was not the sharpness, but the Loca.
I'm not a huge fan of DXO's lens tests for sure as I think their baselines are often off, but they are standardized so at least you can see what the strengths are across lenses are if it is even shifted.
That said, I was surprised to see the low CA on the 1.4g - your shot of it looks just like what I see out of my 1.4 with CAs and thought the newer 1.8 was better than the scores state. I also thought the Sigma was much worse than what they show as well.
Personally I do not mind the Green CAs of Nikkors as I find that much easier to fix or less noticeable. Sigma lenses tend to have an almost neon green and/or purple/magenta CA that is an artifact of the glass they use. I find those colors more difficult to handle and more noticeable.
...What makes sigma 50mm so popular among pros, just this what You mentioned Tao - maximum quality at 1.4. If I'm buying a 1.4 lens I'm getting it for one reason only: I wanna shoot at 1.4. If I would like to have a cheap travel lens, than I don't need 1.4 and can get 1.8 instead, and can stop it down to even f8 - like in the old times, f8 and forget.
This is exactly why I keep looking at one year after year but when I look at my data from my shots, and in reference to another thread, "Portraits - f-stop and eyes in focus"(http://nikonrumors.com/forum/topic.php?id=15698), I am almost always at an angle and shooting at f/2-2.2 for the DOF to keep the eyes sharp across it. By that time the gain just isn't worth the cost. (Dang rational thoughts - I like to get shinny new lenses.)
I love the idea of the Zeiss Distagon 55mm f/1.4 ZF.2 (have you heard is it AF or MF only?) but the price tag of $4,000ish is unjustifiable for me personally. There comes a point when the gains are so small and the majority of my work's end result is doesn't bennifit from it, the cost is just a desire rather than a "need." It would be fun to use though!