300F and the transmission fluid is rated to last about 50 miles.
275 and it is good for something like 2000 miles.
Below 230 is what you are looking for, that is good for the normal 15,000 mile service life. When you start to reach 230, it is time to slow down a bit. Perhaps shift into a lower gear, the transmission will pump faster through the coolers, and the fan will speed up, cooling the engine a lot more.
215 is normal range while not towing or climbing hills. 190 is also great temperature. 180 is about the minimum that you want to run on a regular basis. Something like 160 will not be warm enough to boil out any condensation in the fluid, leading to the need to keep it at 180F.
In the winter, you might not see it reach 160F on the short drive to work, so it might be wise to drive it a bit further once a week or at least once a month to warm it beyond 180F for about 15 minutes to drive out any excess moisture.
Fred.