The best thing you can do is use the immersion chiller to drop the temp in the kettle to about 140ºF, then run it through the plate chiller. You'd be able to run the wort through the plate chiller at full speed if it starts off at 140ºF.
Remember, getting the temp of the wort below 140ºF as quickly as possible is important to reduce the DMS in your beer, and for preserving the aroma of the last hop addition.