Zurb vs. Bootstrap themes: About performance
The Drupal Bootstrap is just a wrapper for the Bootstrap Framework. When you download that, the compressed size increases by about 200 Kb.  However, I don't think size is a good metric for theme performance.

Foundation has a very limited number of UI elements, it just gives you the foundation to build your own theme upon. Bootstrap provides almost every UI element you can think of. If you want to design your own CSS carefully, to give your site a personal design, go with Foundation.  If you just want to do rapid prototyping or to have  a responsive site up quickly and with little effort, go with Bootstrap.

As for performance, I haven't spotted any clear differences between these in the context of Drupal. Btw.: I don't think the Drupal versions should differ from those on other platforms, as most of the code is the same for all platforms. The Drupal versions are just wrapped to fit into Drupal's theme system.