Yes JimF, you've really got it!
To add to the anecodotal evidence, I ran 80/20 water/coolant and one bottle of WW on our vacation to Las Vegas last summer. The E500 endured 120 degree heat, a day of racing at the track and another day of top speed running down the highway...140mph with air conditioning! The temp gauge stayed within it's normal range all the time...and I'm told by others that is a little unusual for the M119.
I'll be adding WaterWetter again this summer for sure