Most Helpful Guy
That seems like a lot of work. Why don't you do it and tell us what you find.
For the record, my bet is on 'medium' though it depends how you measure the categories.
When things are -very- mixed, everyone's different, its just how things are.
When its very homogeneous, there's little opportunity for issues.
When there are a few large groups, or a large group and a very identifiable minority group, I suspect your potential for 'us vs. them' is highest. In the very high diversity case, there's no 'us', in the very low diversity case, there is no 'them'.