2006 E350 (W211)
While you might get an extra 1/4 to 1/2 mpg (max) running your tires at 45 PSI, you’ll be rewarded with substantially diminished tire mileage as they wear down the center (not to mention poorer ride quality and potentially worse cornering) the cost of which will dwarf any savings in gasoline.Personally I would leave everything as it is with the idea of doing something to what you've got .
I've got a Sept. 1991 built , sold in 1992 560 SEC . Didn't want to add anything to it that wasn't what came from the factory , with an exception :
I first changed the oil over to pure synthetic ( 0-40 ) then put a K & N air filter in the housing , 3 prong spark plugs of the highest quality with high quality wires , a copper pick up distributor cap / rotor then put 45 lbs in the tires (not recommended on rainy wet days ) for cruising and distance driving only . Make sure your fuel filter(s) are new and just doing these few things you will notice an increase in its response and pep . Plus better mileage .
Just something to think about .........