Reading through this thread, and having used both lenses extensively, I find that they cannot be compared to each other straightforwardly.
Adam says that the Sigma is the better lens, but that fully depends on what you are after. The DA560 totally beats the pants of the Sigma 500 for straight out of camera contrast and color. You can post process the Sigma images into wonderfully colorful images with enough contrast most of the time, true, but that does not take away from the superior performance of the DA560 in this regard. Also, the DA560 has a clarity and cropabbility esp. with distant subjects that is far beyond what the Sigma can produce. I've spent many hours shooting distant birds on grey clouded shores, and the Sigma is no match for the DA560 here. I've also some A3+ prints next to some prints from the Sigma, and the certain clarity and handling of light and color from the DA560 stand out, as well as does the finer detail that the DA560 resolves. The Sigma is in this regard more of an old school lens, with typically sharp edges, but not the really fine detail resolving ability of a modern designed lens like the DA560.
The prints from the Sigma simply don't have the same level of clarity, and the print quality matters.
On the other hand, I could also find as many reasons why the Sigma 500/4.5 is the better lens. It suffers far less from purple fringing, that can heavily affect a shot with the DA560 when strong light hits a bird sideways and/or reflects of the water. The DA560 also has some of the familiar green/magenta bokeh/color fringing, that is far better corrected on rhe Sigma.
The Sigma has faster AF on the K3, but makes one hell of a racket when tracking in early morning silence or even in a crowded bird hide.
There are many more differences between the lenses, so it's a fully subjective choice i.m.o. and I can not agree with the statement of either lens being the better lens.
I know that my choice would always be the DA560.
Chris
Last edited by Chris Mak; 03-24-2016 at 10:44 AM.