Not sure if this case matches your situation.... but a few years ago I read comments that claimed a country specific website should be hosted in that same country. At the time I had a Florida site hosted on servers here in Australia.
I changed to a USA located host and there was a very definite improvement in traffic numbers.... no significant change in rankings for the trophy terms so I'd say the improvement came via long tail searches.
Make of that what you will. No guarantees given or implied.