Wheels and/or tires question - what to change for better ride?


First, has anyone replaced the run flats with standard tires on the 20" rims? Same tire size as OEM or different? Did it make a big difference in ride or not much?
Second, as an alternative, has anyone downsized to the 19" rims and tires? Same questions - same size as OEM or different? Ride differences?
Finally, I've been shopping for OEM wheels or wheels and tires on E-bay, thinking about if I changed would I sell mine and buy the smaller ones? Just wheels (probably) and then new Continental ExtremeContact dws06s. Or should I find somewhere to trade wheels and/or tires?
I'm pretty much a buy stock and keep stock, but these are challenging, particularly since none of the local Mercedes dealers can get it in to fix the tire or wheel for a week!!!
I have the same wheels on my E-Coupe.
I installed the S-class tires and it provided significant comfort and protection.
Sizes are as follows:
245/40/20
275/35/20
Good luck



