As a quick suggestion - instead of stroking the selection, turn the selection into a path and stroke the path.
I have discovered that this seems to give significantly better results. (The conversion to a path does some bezier interpolations around the selection that seem to prevent some "jaggie" artifacts that stroking a selection seems to have.) Now this might not matter when the jitter is high, but try it and see if there is a difference.
-Rob A>

