Nice glob!
The rough rule is supposed to be guide down to roughly one third the focal length of your imaging scope or something like that, saying that I guide quite well with a modified finder scope on a 900mm FL refractor.
I think it gets much more unforgiving when you are +1000 FL
The image scale becomes an issue as well if you use a small finder as guider but then try and guide a 2000+FL scope.
You can try binning the guide image but essentially the rule of thumb keeps you happy.
keep em coming'
Graz