Hey Kim,
Great question. We have a global business and have seen that our international emails perform better when we send them very early in the AM our time so that they land in international inboxes at prime email open times overseas.
Our approach has been to split out by streams in most cases, but it depends on how intricate your engagement programs are because you are limited to 15 per program. A good rule of thumb - if you think you might have at least 6+ seperate tracks for just north america in a single program, you may want to consider seperate programs because you double the # of streams with every INT stream you create.
Otherwise, we split out streams by NA vs INT and set the cadences accordingly.
Good luck!
-Gary