I personally think constant shifting is more detrimental than heat spikes. In every vehicle I own, if the trans is shifting from OD to 3rd or 4th and back often, I drop down a gear or 2. In my Astro I run in 3rd much of the time if I am under 50 mph. No need for OD at that speed. It just lags the engine and the constant shifting under load creates heat and wear.
In my 2003 Ram 2500 which has the Hemi engine and 5 speed auto, I put a sensor in the test port as well as in the hot line going to the cooler. I switch between them and find there can be a great difference. The hottest I have seen is from the cooler line and it went a little past 250* but the I was towing our camper in city traffic on a 90 degree day. Once on the road it cooled right down to 170* and stayed there. This temp will change quite fast. The temp in the test port will not as it is more of an average. Any monitoring will be a plus so location is not all that important.
Basically, put the sensor in the test port and when you see 200* start letting off a little. If you run full synthetic fluid, 200* isn't as much a concern as the fluid won't break down. Once you have the sensor in and start watching it, you'll get an idea what your trans is doing and how hot it gets how fast as soon as you start hammering on it. You'll find the slow down point quickly.
The rest of these guys are making it confusing! 
and don't earn the big bucks to speak in elegant terms like you. 
)
LOL
