Watching @Thomas_Sanladerer 's video (edit : just a post with pictures, I wrote video just because he usually makes great videos :-)) about improving print quality of PLA with a fan I also added a fan to my CoreXY and it extremely improved the quality of my PETG prints. Overhangs print really well now, and stringing has dissapeared completely. You cant even see the seams where the hotend moved between parts, i.e. the eyes of the frog or the ears and the tail of the cat. On the treefrog i can actually see the polygon edges on the belly 
for the first 3 layers i let the fan off, after that it runs at minimum 30% all the time (faster if nnede by the slicer), it also helps alot at the infill and, of course, bridges.Printed PETG at up to 60mm/s, 0.1mm layer height.
Nice. But wheres dat vid? Must look for it NOW. Iam not printing pla btw just foe fun xD
That frog always pissed me off after printing it because I would always get stringing around the belly. The belly layers were never quit right.
@VolksTrieb ups, sorry, no video, just some pictures : https://plus.google.com/+ThomasSanladerer/posts/jDAmFsMHypb