For what it's worth, I find that accessing Netflix is much faster through a US or European IP. I get "loading" icons for two or three minutes when I try to sign in with a Dominican Republic IP. Using a U.S. IP, sign-up speed is almost normal. I don't see a big difference in the quality of the streams, or haven't so far, but am assuming that they are on different servers.
The other difference is in the availability of subtitles. If you watch Amores Perros from a U.S. IP, you'll get Spanish audio with English subtitles. If you watch the same movie from a Dominican IP, there is no English subtitle option.