Normal operating range is approx 200-250f. It is best to have it above 180 to help insure that acid due not form from condensation as Sul indicated. With good oil up to about 280 range is fine. Synthetics will hold up better than dino for temperture stability.
If you add and oil cooler, will help while moving, minimal to none will sitting still in traffic (other than more oil capacity which will take more time to heat up). If oil cooler is installed, be attentative to not letting it get too cool for than you have a chance of any mositure from condesation not be dispersed and more chance of acid.
A oil temp gage installed in line will be more accurate and give best info verse a tank gage.
If one does find themself having possibly overheated or pushed the limits, it is best to change out the oil ( IMHO ) as soon as practicle to insure that your have fresh oil that had not broken down.