I may not make lot of M.B. owners happy, but taking into consideration your concern about A/C, beware: A/C systems are not M.B.'s forte.

I have owned Mercedes-Benz for 18 years and none of the cars that I owned have/had a decent A/C system, not even my 1998 S320.

I had a W123 (or S123 to be exact) 300TD which, as you guessed it, was hard to cool down at high heat.

In terms of interior volume, I guess a W123 sedan would be easier to cool than a W126 S-class, but then, the S-class comes equipped with a higher capacity A/C. My advice would be to test drive one in a really hot day and see if the A/C performs to your expectations.

A. Rosich
S 320, 1998
E 320 T, 1995