Adding an indicator to a buffered XY Graph that displays data in "real time"

I have a buffered (5000 data points) XY Graph that displays 2 plots as a function of distance.  I would like to add an indicator (cursor?) to the graph which moves along the plots to indicate the current position.

I tried adding a cursor and updating its position with a property node as the position changed.  However, the position changes rapidly and the data needs to be displayed in "real time".  When I update the cursor dynamically with a property node, it slows down the display until it is unusable, for all intent and purpose.

Ideas?