If my only option exporting photos from the newer version and losing all metadata, and then importing into the older version?
You don't have to lose all metadata - in fact you can lose none, except Faces.
This User Tip
has details of the options in the Export dialogue.
An earlier version can't open a later version's library. Not every version of iPhoto will run on Mavericks, so you might be between a rock and a hard place there. That said, you can revert a library with iPhoto Library Manager - see the Help on the app for details.