Very nice Terry :-)
The lens seems to have a pretty nice image quality.
I think the only way to get maybe a little bit more details would be with some kind of contrast filter in front of the lens. But I think the increase would be minimal. Maybe the details would also be less due to the longer exposure time that is required and the atmospheric disturbances.
True maybe a blue/green filter might help with resolution/contrast a little. Hmm, might have one of those :)
I think it would be interesting to see if it increases the details or decreases them due to more glass in the optical system or the slightly longer exposure times.
Some years ago I made a comparison between the 100-300 f4 sigma and a 1000 f11 achromatic refractor. The Sigma lens had much more detail even with just roughly a third of the focal length. This was caused due to the chromatic aberration of the refractor and the atmospheric disturbances that are more visible at 1000mm. Also, the optical system in the lens is way better corrected and coated than an achromatic refractor.
Check out the Sigma 170-500mm version I just added above.
The quality is very impressive. It seems to be almost better than with my 420mm APO refractor.
This is a single shot of the Moon with the Sigma 100-300mm F4.
The image was taken with my Nikon D7100 1/200 sec., ISO 100 and the Sigma lens @300mm f6.3