Just opened HWMBO workshop manual for 4 series Perkins and it says :
Indirect cooled engine - Thermostat opens at 69C, fully open at 87C
Direct cooled engine - Thermostat opens at 52C, fully open at 66C
(Page 27 of Manual)

Page 88 of ame manual indicates that your system is a later one with pressure relief system to allow water to bypass closed thermostat. The engine is designed to run at approx. 60C to prevent build up of salt deposits in head and cooling channels. Older engines on direct cooling had a manual valve you could adjust to control temp.
Indirect or Heat Exchanger cooled engines are designed to operate at higher temps of 65 - 93C.
It would appear then that you may have a higher rated thermostat than Perkins reccomend.