"I don't agree with the idea that overloading tires means imminent tire failure at high temperature and speed as I've found there to be a pretty large safety factor incorporated into tire ratings. "
Tire rating really don't have any safety factor designed in . But it's important to remember that heat is a function of Loading AND Speed. Most of us are not running at full loads anywhere near max speed ratings (which are validated for 30 minutes). On that note... Ford worked with Continental originally to produce a 19.5" tire with a a higher speed rating, specifically for the F450, and now other tire makers are matching that. The original F450 was governed at 75 MPH due to the tires, which caused some buyers to "downgrade".