Sorry to disagree - but I do...... my Thunderbird - in good mechanical condition runs 100º-105º over ambient ( right down to the thermostat setting). On a very typical summer day here - 105º ambient - that's 210º. That was probably getting up near to lubrication trouble in 1956 - but not in today's oil formulation. If the coolant mixture is correct - and the pressure cap the same as OEM spec - I'd say the internal conditions are still physically within the OEM design pressure parameters. If there is circulation reduction (or gunk in the block or radiator) - different story. 

What none of us wants is a "boil-over" where the amount of flowing coolant is being suddenly and drastically reduced. It might be HOT at 210ºF but at least the cooling system is still working on rejecting the heat and not losing its fluid capacity. If you need to stop driving and let the cooling system do its thing to drop temperature - you can do it.  
 

 
 Steve Metzger       Tucson, Arizona

The other thing I"d add is to go buy an inexpensive infrared thermometer. I've got a couple of them, and mine have read within a degree of a really expensive Fluke. The won't take a beating, you have to take some care with them. But it will tell you the temp at the tstat housing, top tank, bottom of radiator. Let's you know where your in car gauge is really reading.

Typical examples at Amazon.

https://www.amazon.com/s/ref=nb_sb_ss_sc_1_7?url=search-alias%3Dgarden&field-keywords=infrared+thermometer&sprefix=Infared%2Caps%2C262

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

Nice, I like the back and forth discussion. I have one thing to add.

I've got a reprint of the original service manual. In the part for Thermostats it lists two a normal and a hot setup. Normal opens at °180 and hot opens at °200. Now if °200 were too hot for those engines why would the book even list a thermostat that hot in the first place?

Roger,

One of the problems with our 'birds is getting the air out from under the hood. In a parade, many pop the hood open. I've done that stuck in traffic, and even from behind the windshield you can feel the heat hit you on a still day. Some headers make that worse, putting a supercharger or a/c unit makes it worse. But you can still control it if everything is up snuff. Hotter than you'd like, but inside my limits.

The high temp thermostat was probably for extreme cold. You really needed the heater at 20 below.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ