With thanks to Paul of Pauls Studio for enlightening me - because I had not noticed!
Call myself a Social Media Manager, tsk... :)
Find Your Most Popular Post
If you hover over the stat which shows the 'number of people who saw this post' at the bottom of any status update, a pop up box will appear alerting you to the stats about the organic and viral reach of that post.
If it was a Promoted Post, you will also see the Paid reach.
At the bottom of the pop up box is the legend '*** people saw your most popular post' with the most popular post part hyperlinked.
Click through and it will take you to the status update that achieved the most views.