iPhone with IOS 5.x allows downloading of favorite contacts only to the sync phonebook.
I have 2013 Ford edge with 4.7.x sync (non-touch) and iphone 4s.
The key is to set it on the iphone's Bluetooth settings for "sync". Enable favorites and don't check "All Contacts".
The "Other Groups" setting implies you might have more flexibility but none of my Outlook groups showed up as an option.
I could not get "push contacts" or Ford's "Sync My Phone" to work (files get generated to the thumb drive, but Sync didn't like the signature).
Suggestion to Ford: Make a rudimentary contacts import a part of the Sync platform. Then users would have a lot of control over what gets sucked into the Sync phonebook.
My Outlook contacts, 1200 entries, has too much private data to be sitting outside all day and all night in my car. By reducing the phonebook to just favorites you get better performance on the voice recognition. As you can tell I went the long way around to get to this solution -- finally saw the link on the Ford website. Can't find it in the user's manual.
http://support.ford.com/sync-technology/phone-compatibility-sync#reload