By ultimate star test, I mean that I'm using the Star - our Sun. :-)
The sky was no good today, but it's doable. First up is my Borg 45ED II, and the sky condition was the worst by then. Next is my Orion 100ED with cheapy-ERF, PST etalon, 2.5x binoviewer corrector and a BF10... Finally is my C5 with the new DIY motorized focusing, cheapy-ERF, PST etalon, and a BF10.
Borg 45ED II:-
Such a long OTA of the Orion 100ED is proven unuseable indoor, even when I've tried all sorts of angles and combinations, part of the aperture were still blocked and the room for slewing is essentially zero. Anyway, I took a few AVIs with it despite the aperture is at least 40-50% blocked.
Orion 100ED with PST etalon and BF10:-
However, the C5 works perfectly with some rooms to slew around.
C5 with PST etalon and BF10:-
I can already conclude that the C5 is the best thing for indoor purpose, if I were to stick with a GEM for tracking, altazmount could be another story.