I have found the QHY9 preforms well in relation to filling up the wells when calibrated correctly, This image i think only got unto 25k adu though the brightest part of the nebula and only the brightest stars saturated the well, I will endeavour to take a screen shot of the un altered raw fit file for you to have a ponder over.
Im quite spoilt that my back yard is dark skies i pay for it in travel times as im on the train commuting from uni to home for a good 3 hrs a day
But as you want more and more long exposure mega data images you have to split your imaging time up over days. For the most of it I run on each target for about 3hrs a night and do between 2 and 3 targets per evening, only due to the location of the image. So i try and capture the shot for 3hrs coming unto the meridian, then keep moving back for another 3 hrs. eg, so i don't have to flip and my kit is balanced and calibrated for that part of the sky. At best i only get to about 35-40 degrees from the horizon so horizon isn't that much of a issue.