Jim,
Nice capture - that is pretty darn good detail for a single image capture. As Alan said, you could experiment with boosting contrast a little more, and see where the image starts to break down. Of course, since it was not night time, I would not expect a black sky. And in point of fact, even in the middle of the night with no moon at a dark sky site, the sky seldom renders truly back, as their is frequently airglow, and often still some detectable light pollution that crops up, although not in short exposures like this.
The Sigma 150-600 will help with your scale too, especially in crop mode. I bought mine about 2 months ago when they were on a screaming deal, primarily to start dabbling more in wildlife shooting. But for moon and sun (with the right filter!) stuff it can be fun as well. I have not shot star fields with it yet, but I am betting it might be somewhat rough in the corners, especially wide open. And of course for the longer exposure deep sky stuff, f/6.3 is not super fast. But well worth trying out, and no doubt capable of some very nice results especially on stuff like the moon I would think.
ML
