If what we care about is latency (and the difference between client and server), why would you plot latency on the x-axis (which by convention is the independent variable).

Rotate the axes -- then it becomes obvious that some fraction of the time, the differences between client and server wait times grows large. Don't make the viewer have to figure out that what matters is the distance on the x-axis. Put the thing you want to focus on/minimize on the y-axis where it belongs.