So what temps are to high to continue wheeling? When should I shut it down and let things cool off if it ever gets to the point.
Personally I slow down or stop when wheeling and my Coolant temp hits 236*F. As for the trans temp most companies who warranty re-manufactured transmissions will void the warranty if at any point the trans temp has hit 260-265*F. I have had trans temp gauges on my autos for years now and have learned to not be concerned about it went its 215*F or below. 217*F and I am pushing a little too hard for too long and need to back off.
Edit: The only time my JK has hit 236*F was when I lost the serpentine belt, was driving in 4Low at over 3000rpm for more than 5 minutes straight in almost 100* weather, and when I had a front brake caliper seize while driving causing the Jeep to hold a lower gear and increased load on the the engine.
That last incident I was glad that I had my Trail Dash set to alert me when my coolant temp exceeded 235, it let me know something was wrong and it wasn't my imagination.