You don't need big long focal lengths to get decent detail in your galaxy and PN (or any other object) images, just match the focal length with an appropriate size pixel, buy the largest aperture you can afford, then be lucky enough to have some reasonable seeing, easy
To add to the other good examples already posted too ilustrate what's possible (I second looking at Lee Borsbooms images!), the following extreme close up crops, were all done at the native prime focus, 1120mm FL of a fast 12inch F3.8 Newt, with a small pixel camera, providing 0.84"/pix image scale (no lucky imaging used, just straight 5-15min exposures, stacked), from just outside Canberra, so reasonable seeing conditions generally.
As you can see, plenty of detail can be discerned
NGC 6872
Shapely 1
The Southern Crab
NGC 1566
Good luck with your (confusing
) quest
Mike