DuckDuckGo's control definitely wasn't adequate, but in return Google's examples ('football' and 'Paris') have unambiguous localization value that's not present for two different Americans searching "immigration".

Quite a lot of the variance was link reordering and result changes that didn't have any clear regional aspects, whether at the domain or story level. If localization is the active factor, it's still pretty interesting to know that where I live determines whether to show a Wikipedia link and how to order HuffPo against the Tribune.