I think mine was around 2000 to 2200 or so, IIRC. I know to get it to run OD at 55 I had to get up to ~60 and then back off.
One sure way to tell if you are in OD -- there is a switch on the console that turns the OD off. It has a little light that will come on when the OD is off. If you are in OD and turn it off, the RPMs will jump up a couple of hundred as it kicks out of OD.