When I bought my 95 E320 new in 95, the dealer always put in 10-30. And this was south central Texas (San Antonio)...doesn't get much hotter anywhere in the US.
And this is what I'm still putting in both my E320's with a combined 210,000 miles...never a problem and neiither one use any oil.
I see the recommendations now for 10-30 say -4 to 50 degrees.
What has changed I wonder?