most have estimeated above 6000
possibly more
IIRC a default rank of nothing puts you in the middle, or at least it seemed so a few years ago. back then a no rank = 2500 or so, now it's above 4000
the reason i think its the middle, if you go first day of month, do REAL bad, IE kill nothing get killed 5 times, and make all bullets miss, you can drop rank below what it was to start with
i may be totaly off though