We have been steadily upgrading all our Drupal websites - (ours and clients) in the last 2 weeks.
The process has been slow for numerous reasons. First I have had to do paying work at the same time and second each site needs to be done twice - we have created a test server that mirrors as closely as possible the live server. On this test server we upload a backup of the live site, test it, perform the upgrade and test again. Then once we are happy we push the live site into maintenance mode, upgrade it and test it before going back online again.
We had Drupal websites in 4.5.2, 4.6.3, 4.7.4, 4.7.5, 4.7.6 and 5.2.0 versions.