multi-db or not

It is a little confusing that the information page said:

However, when you get to a few hundred sites, ... things can start to get a little cramped inthere as your database now contains thousands of tables and quite likely a fair bit of data too.

But the intallation page says:

1-5,000 blogs/sites you should be fine with your WordPress default database

The information above is kind of conflicting...

I would like to know if I plan to host 1,000 sub sites, how do I decide? multi-db or not?