Ummm, remember you could be seeing nothing more than a discrepency between the accuracy of the guage and the accuracy of the sending unit. If the guage is off o the high side and the sender is off to the high side, you might see a reading higher than actual temperatures.
With that said, I run 209*F (via a Granatelli Monitor) in 100*F weather unloaded, stock tires, cruising the highway at 65mph. I have "spiked" at well over 230*F (236*F), trying to regain momentum lost on a hill.
I have seen EGTs spike at over 1500*F for a few seconds (under load, usually coming out an offramp), average around 600-800*F depending on speed.
And all this is with a stock truck that I have ran this way for over 130k... and only recently installed the monitor to see what is really happening.
steved