I had problems with the printhead dragging along the print surface making a very rough print. I began using Slic3r with 0.02 z-offset instead of Cura and the problem disappeared. With printspeeds over 50mm/s the PETG filament has a hard time extruding at enough fast pace, best print quality is achieved with 40-45mm/s printspeed (stock hotend, no print-head mods). I use Prima Select PETG at 240-245C, I have been using 5-7mm retraction at 40mm/s retraction speed. Used both 0.20 and 0.10mm layer height with excellent results. First layer hight 0.20-0.25. Only use the fan if the object is small, lager prints don't need a fan unless overhangs or bridging.