Would I be right in supposing that if I like large detailed planetary views...
Other things being equal....
1 - magnification is dependent upon light path length a 4.5" f8 gives the same magnification for a given eyepiece as a 9" f4. (of course the 9" object will not dim quite so quickly...
)
2 - short newtonians are not the best really here but do enable you to look at large dim objects with large fields of view for when you tire of planets...
3 - Brightness not withstanding, exit pupil puts a downward limit on eyepiece size (aperture in mm/magnification) - 0.5mm being about the usual limit until floaters etc start being a real problem
4 - larger apertures for a given length mean larger exit pupils and more likelihood of keeping it into the normal range of 2-5mm for a given eyepiece.
5- If the mount cannot track Saturn whilst viewing it at x300 there is no point anyway, likewise if it blows in the wind, you cannot see it.
6 Is it practical to actually view planets at high magnification without motor drives and using slow motion controls - it does not seem likely to me ?
cheers