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I run stock and water temps stay right around 190-200 based on my PCM fan settings. On the track (road course) temps never got above 210 for me.. and that's in Florida/Lousianna in the summer, so its quite warm. I have the Dewitts radiator as well. The upgrade is the radiator, the thermostat is not some magical fix....IMO.
BTW I have a brand new OEM t stat waiting to on the car. For fun I put it in a pot of boiling water. At my elevation, boiling temp is around 200-205F. And at the temperature, the thing was fully open. So unless you want to run something colder than that, no reason to change it.