I'm sporting 17" rims on my 93 300E. I kept the stock width and profile with 40-series profile tires. Tire dealer originally opted for 45-series, but they rubbed when cornering and hitting bumps.
I haven't noticed a big difference in ride quality, but you do have to be extra careful around curbs...you can really trash rims!!
Also be prepared to replace tires every 18 months. Most low-profile offerings are a sticky compound, and won't get you 50K miles of use.
Note: My car has the stock ride height...
Rear wheel clearance:
Front wheel clearance:
