Did a couple of test prints with the saintflint extruder. It works very well, of all the 3d printed extruders I have tried out I rate this one the highest. Has a lot of grip on the filament without deforming it and it can handle fast speed printing.
It’s easy to print and assemble. I’m using a hobbed pulley that I found on Aliexpress and a Kysan stepper motor with decent torque.
http://www.youtube.com/watch?v=iKFkm_s_ZR4
How much torque does your stepper has?