So started doing some aggressive retraction (12mm) while printing some Fire Red NinjaFlex. It’s so weird watching the printer and listening to how different the sounds of the printer on. With retraction set at 40mm/s the hot end stops and waits for the filament to move up and down. It isn’t something I’m used to hearing/seeing and it really throws off my groove. lol. BUT the prints, so far, are turning out fabulous with practically no stringing. Printing out new Printrbot Metal Simple stabilizer feet (the last ones didn’t fit too well) and then I’m probably going to go for a pair of Adafruit LED horns. 
Then, maybe, I’ll finally get that time lapse footage I’ve been promising.
I use a couple mm of retraction and have never had to deal with stringiness, but for sure it works the extruder motor.
I’ve tried up to 5mm retraction but I think I had the hot end too hot so it didn’t help much. I’ve since then been printing at 240C I get stepper skipping with anything less. I’m starting with the extreme as far as 12mm retraction is concerned (I saw this suggested by one of the engineers over at Fenner as a comment on a NinjaFlex review). I figured I’d try the suggestion and dial it back as far as I can while still getting good prints.
I just wish I had more of this stuff to play with.