Bowden Extrusion w/ 0.25mm Nozzle

I'm in the process of getting my Rostock to begin its first print but I have been having issues with my extruder (you can read about it in my thread). This thread is about gathering information on bowden style extrusion particularly with smaller nozzles like a 0.25mm makergear hotend nozzle.

Using a smaller nozzle introduces bigger slack back problems in the bowden tube tha can be compesated by different retract lengths/speeds or perhaps a tighter PTFE bowden tube. I'd like to hear about other folks using bowden extruders with small nozzles, I want to know what retract lengths, and slic3r settings you are using as well as Marlin firmware tweaks to gain consistent extrusion with 0.25mm nozzles.

BTW I am using 1.75mm filament PLA plastic.

Calibration is as simple as making a program that goes through a range of retract lengths/speeds and visually verifying that the flow indeed does stop when the nozzle is floating in the open air and that the flow starts back almost immediately when you go to extrude again. I wouldn't try anything fancier than changing the retract lengths and speeds. It is my experience that you can find values that will make you more than happy and those are easy values to mess with. (I have a .4mm nozzle and I use 5mm retract at some speed I have forgotten. The tube is somewhere on the order of 600mm long.)

Additionally, Slic3r has introduced some features that are suppose to make bowden printing easier. "Wipe" is something to check out among other things. A google search for "Slic3r settings for a bowden setup" will also give you lots to think about.