I've gone back and forth and the downgrade works fine. It's still with the Keynote 5 family.
Here is the procedure reproduced from up above. I am reproducing it here with full and due credit to the original author as a convenience. Bear in mind that this procedure downgrades the entire iWork '09 suite: Pages, Keynote, and Numbers. This means that none of these applications will have the autosave/versions feature of 10.7 that is troubling Keynote.
1. Remove iWork 9.1 using the Apple script supplied by Yvan Koenig. <http://public.me.com/koenigyvan>
You can also find the link here: https://discussions.apple.com/thread/3272551?answerId=15969759022#15969759022.
If this link doesn't work go to the iwork discussions and search for Yvan's name and the word "remove". It will get you to a post of his with the link to the script.
If you do a manual uninstall you will have to do more than simply remove the iwork folder from ~/applications. Try using easyfind to locate all iwork files. There are many spread throughout your system. Make sure that the following folder is uninstalled before you reinstall the earlier version as a reinstall of an earlier version will not overwrite them. ~/library/application Support/iwork '09/Frameworks.
Also check ~/Applications for a residual iWork'09 folder after running Yvan's script and delete it.
2. Reinstall iWork '09 from a valid iWork '09 installer disk.
3. Update iWork to version 9.05. You can get the updates here. http://support.apple.com/downloads/#iwork. There are four update packages: 9.0.1,3,4 and 5. Execute them in order.
4. When you launch Keynote, check the version number to make sure that it has been successful. If you reinstalled without a successful total removal it will still show version 5.1. The script mentioned in #1 above does not remove your personal templates stored in your user/library/application support/iworks folder.
5. The first time you open an iWork app it will ask you to upgrade to 9.1. Do not do this and check the box indicating not to be reminded again.
Be careful that you do not unintentionally update with a hasty click of Software Updater. Deselect the automatic download feature in its preferences and check the list before updating. Also, as #5 indicates, watch for the offer to update the first time you open Keynote or you will quickly find yourself back at square #1. I've done this.
I've done this now several times on two computers. It works quite reproducibly. I am currently working two large Keynote files with several imbedded videos without problems. I wish that Apple would make the autosave/versions a switchable preference option. It works well with Pages, not well at all with Keynote. It wouldn't surprise me if large spreadsheets with calculation fields suffer similarly in Numbers.
Message was edited by: William C.