This is more FYI. I had a very odd customer with 12k contacts! GO would not import all these, it would halt.
I know it's very uncommon and no big deal (even because customer didnt even knwo why he had so many contacts, prior owner of account perhaps was doing email marketing or account got abused), but just FYI, since, after all, one might have many many contacts. Gmail, for example, asks you to split files in 12k contacts and is able to import it just fine.