Originally Posted by vdbucks

See my post above... noting specifically the "'meta_key' => '_thumbnail_id'" in the query args...

If, however, you want to discard all other post data except for the featured image info, then you'll have to do a more advanced query with wpdb, join some tables and such... I could give you an example if this is what you want to do, but to be honest, the savings in overhead won't be that great compared to just running a normal query like I gave you above.