I think that is where I'm leaning towards. I have not used the Sigma but like the idea of the 77mm filter size to make my filter bag to a minimum. Since I will always have a camera with a AF drive, I'm not particular one way or another. Surprisingly my non-D version is much slower than a "D" version.
Interesting on the Sigma. I have yet to hear of anyone who kept theirs. Many have used it and sold it.
The problem with Sigma is that it has more purple color rendition in my experience. While it's not that much of a difference,it noticeable which picture was shot with a Sigma or a Nikon lens. Moreover if you are building a camera system, logistically speaking having all the equipment(DSLRs and lenses) of the same brand is just so much easier and hassle free.
I compared the Sigma 50 1.4 to Nikon 85 1.4 af-d. It's heavier and bigger than Nikon 85mm. Because it has a 77mm front lens element it's super heavy for a prime. But one pro of the Sigma was that the AF was super fast.