Here's a quick breakdown..
Site managers have all permissions listed under Content Editor as well as those listed under Site Manager.
Content Editors
- Administer blocks
- Administer block classes
- Manage Webforms
- Manage menu structure
- Manage content
- Use any allowed content type
- Alter url aliases
- Use contextual links (gears)
Site Managers
- Able to add new users
- Manage user permissions and assign roles
- Able to alter default contact webform
- Able to alter site configurations
- Able to administer theme
- Utilize administration pages
- Manager and alter vocabularies (taxonomy)