Tire Width question
 

05' W211 E320 CDI


I recently picked this car up and the previous owner put some factory Mercedes bbs 17" wheels instead of the standard 16". This means the tires are now 245/45 17 instead of the standard 225/55 16. Since I'm not looking for performance out of a 4k lb diesel but rather economy I am wondering if I should put some skinnier tires on.
The increase in diameter is a good thing for fuel mileage but not the increase in width and weight.
What is the most acceptable skinny tire to put on a 17x8.5 rim without compromising too much on ride and safety?
I imagine a 225's would be a bit stretchy though I have seen winter wheel combos running that size tire on a 17x8.5...
235's would be easy but would it be skinny enough to be worth it?

Once a size is determined then I need to find the right tire. I am a big fan of the LRR (low rolling resistance) tires, and particularly the little bridgestone ecopia's on my gf car. They do make them in the correct size/speed rating, but not sure on the load rating and ride quality on a heavier car like the E class.
I hear a lot about the extreme conti DWS all seasons being excellent and they do run these sizes as well but I don't believe are LRR.

What would be the best skinny size for the 17X8.5 wheels, and what would be the most efficient tire without completely destroying the nice ride of the merc?

Thanks.