225/50/16 will work on non-500 W124's provided the wheel offset (more critical than overall wheel width) is right. This setup is very sensitive to offset. The 205/55/16 (also a viable setup) is not so sensitive. If you are going with only 205 section width just go OEM sportline size and go with 205/60/15. As far as your concerns with curb and pothole protection, buy a tire with a rim protector bar. Ask Luke to recommend specific tires with them but its basically some extra rubber that sticks out further than the edge of the metal rim to take the "hit" and prevent any rim damage.

400E's are stock with the same size as the 300E 195/65/15. This is something that 90% of all 400E/E420 owners remedy somewhere between the 2nd tank of gas and 1st year of ownership. Generally the 300 and 400 w124's can share shoe size. Since this is such a popular topic/mod a search the shop forum for previous references to this topic should turn up a wealth of info. Let us know if you have any questions. As always, it never hurts to get Luke's professional opinion on things.

Hope this helps,
Lee