Just about all the advice you read about reducing stringing tells you to increase the retraction rate as much as you can. In practice, with this combination of a long Bowden extruder and E3D head, I found precisely the opposite to be the case! I got best results, way better than with faster speeds, when using a slow retraction speed of 30 mm/s or less. The 100 mm/s + recommended speeds were awful.
For now, I've settled on 2 to 3 mm retraction at 30 mm/s for PLA.
Note: I'm not doubting that for many machines increasing retraction speeds may be a good thing for stringing, but for my Rostock Max 2 wih standard Bowden and an E3D v6 extruder, it isn't.
