In 1989 the improved Tempfet series was introduced, based on the older Mosfet series but using a new generation of FET transistors. These had an internal thermal protection so the term Tempfet was used now.
Overall these versions were available
ESC-300 Racer (R) as budget version
ESC-600 Pro (PT) as competition version
ESC-600 Pro X (PXT) same as Pro but 3 wire setup for improved efficiency
Jack Johnson of Team Losi used an ESC-600 for winning the Offroad 2WD Modified Nationals in 1989.