I would say set it between 180-190 , that is where i have the fan on my X come on of i remember correctly (its not a Trail Tech , i set mine up before these were available from a Ebay fan (the same fan KTM uses) and Autozone sensor and my own wiring harness) , i have a automotive fan temp sensor/switch that screws directly into the lower right radiator tank where the plug is and its preset to come on at i believe 180 and shut off at 160 if i remember correctly , i have a write-up post somewhere around this site when i first installed it back in 06 or 07 or so , and it tells the preset on/off temps of my sensor , maybe do a forum search for "Cooling Fan for 450X" , and i think it will come up , mine works perfect when riding single track , i have never overheated since installing it about 10 or more years ago
Basically set it at say 180 , if you find its coming on too often in situations you do not feel are necessary , then bump it up 5 -10 degrees , basically you want it to kick on when your going slow (walking pace) or stopped a lot , you don't need it to come on when your doing 10-20 mph as the airflow thru the radiators should be sufficient , i would also recommend installing a 1.6 or 1.8 radiator cap instead of the stock 1.2 , this will help prevent boil overs as well , also i use Engine Ice , and i would recommend something similar like it or Evans Waterless Coolant , it will up the temp before boil over by (Engine Ice for example) 50 degrees , which helps and keeps the fan from overworking unnecessarily and keep the coolant in the overflow tank instead of continuing to boil and steam out the overflow tube on the overflow tank , as once it does that , it does not recover that coolant , so you want to keep it from getting to that point
Hope that helped ...