I have to ask: are you comfortable with using your 10" dob with a 2X or 3X barlow for the smaller DSOs and your Mod-3C? If so, I would go with the 140mm refractor. I am only now getting into a careful comparison of my 140mm with the RC-10 (using the NVD Micro) so I may be making this recommendation prematurely. I just think that there is something special about the 140mm class of refractor. If I had to pare my herd down to one scope that would be it. One thing that I have discovered is that there is an enormous resolution increase when I looked at a bright glob (M5) and went from f/12.5 to f/20. It really transformed the appearance of the cluster, was fully competitive with the views I get with the RC-10 and was easily handled by the Micro. I plan to make more comparisons like this in the coming months.
Edited by chemisted, 23 February 2019 - 07:37 PM.