For the beginning I made two screenshots:
1. Editing a site with acf and flexible content field:
http://de.tinypic.com/r/rhqudy/5
2. After saving the site as revision, the preview in revision manager of revisionary looks like this:
http://de.tinypic.com/r/2djdnrp/5
What can I all test and report to you to speed it up? 🙂