How hot is too hot?

[Racer Boy]

It may show slightly hotter than that during your sessions, if it gets much higher than that, back off for a lap and see if the temp comes down. If it keeps running hot, you can short shift; instead of 7K, shift at 6K.

Also, really take it easy on the cool-down lap, and once you get back to the paddock, leave the car running for a while. That way it'll keep the coolant circulating, and you won't get boiling in the coolant tank. The only issues I've had at the track have been when I've come in and turned the car off. Twice it's puked coolant from the cap (which I've replaced twice now).

[BoxsterSteve]

The heater core can do a pretty good imitation of a radiator to help pull heat out of the engine coolant.
As an addendum to the leaving the car running in the paddock idea... crank up the interior heat to max and turn the blower fan on full blast too.
You probably won’t want to sit in the car while doing this.

[husker boxster]

You might also want to take a little trip around the outer edges of the paddock before pulling into your pit area. That lets the brakes cool off.