What if we turned the tables and asked for the most US name ....I can think of a few that would be highly unlikely to occur over here in the UK. Cecil for a girl, frex, or - my personal favourite, and I did meet the woman in question - Treelight. Admittedly she wasn't given her name by her parents (it "came" to her in a vision) but it was very difficult to use her name in natural conversation.

I don't think I've ever met a Donny and relatively few Nigels (although those Nigels I HAVE met tend to be good musicians).