Thank you for sharing your experience Lee - your images certainly are great and inspire me and many others
Galaxy imaging is something I would like to do in the future, so this discussion is of great interest to me.
I put together a simple excel spreadsheet in an attempt to
roughly estimate which system would be optimal for galaxy imaging with the seeing we have in coastal Australia.
It looks like my camera's small pixels are always limited by any smallish optics slower than f/6 until we get to 140 mm aperture and above, when seeing will become limiting factor. So for my current camera, either a 250 mm f/4ish Newton or 140 mm f/6ish refractor would do for galaxy imaging, with Newton being significantly faster but would require collimating.
Those two might be my options since I feel that in the future we will see more new sensors with smaller pixels that will most likely will be more affordable than sensors with large pixels.