I think the thermostat temp is about 82 degrees. I have my thermo fans cutting in at around 90 degrees.
The factory thermo fans on the GZ20's cuts in at closer to 100 degrees.
As for the maximum, push it at your own risk. If it gets hot then drive easily and if it still gets higher shut it down.
I would get the cooling system flushed before the trip and make sure it is in good health. While your driving it should keep at reasonable temps, it is idling on a hot day that will kill it.