Well I live up the road from Ismalley and have been through 3 124's in this climate. My experience tells me that you are not going to improve on the numbers. There just isn't enough heat removal for the existing coolant to handle. I assume you have a minimum of coolant and a maximum of distilled water. I run about 30/70 mix as I NEVER plan on being cold again!
I sold my CE320 and bought a '97 CL500 then a '97 CL600. Wow what a difference. The 8 and 12 cylinder engines have a LOT more coolant capacity and it makes all of the difference in the world. I remember last summer I sat in my car idling with the AC on for 15 minutes while an old man unloaded his groceries. It was 118F (hottest day of the year). The temp never got over 95C! I have never seen the temp on either of the 2 CLs exceed 95. I took a run over to Phoenix recently averaging 77 MPH and the temp was about 104F The coolant temp stayed ay 87C (The thermostat is a 87C unit.)
I would not worry about the 124's running hotter. That is just the nature of their system.
Anziani