After weeks of messing around with settings, going over half a dozen of different brand of filaments, I think I have finally figured out the biggest issue of PETG quality (overhangs). It is all about cooling. Nothing else matters as much as proper cooling.
The only thing that people need to change is drop down part fan towards 0 (0-30) and turn on AUX fan (up to 100%). The default is the opposite - part fan high and AUX fan 0.
This could also explain why people are getting different quality results - because some people print in hotter environments and some in colder and some print with open lids and some with closed.
I will make another post when I pull together all data from all brands and see what is really optimal.