Then the stepper was skipping steps. You might try upping the speed in steps to find out where the critical point is. The stepper must decelerate and accelerate a moving mass. As it has a maximum amount of force it can apply, if the speed is too high it just can't keep up.

And yes, you will find that patience is the most influential parameter in getting good quality prints

(...and waiting 8 hours for a print that succeeds first time is less time than failing mulitple several hour prints to find the bleeding edge of what your printer can handle)