just adding my 2 cents worth....
i did not expect it but when i was given the chance to drive a 530 newly installed with 20 inch tires, the difference is like night and day.
I expected super bumpy ride, but this did not happen. It was no more bumpy than a 17 inch tire.
The ride improved with an apparent solidity feeling of the road.
It was no more noisier than the old 17 inch Continental Sport Contact 2. Sometimes the new 20 inch sounded quieter because the noise if any tends to be of lower frequency than the mid frequency produced by the CSC2.
The acceleration seem pretty much the same.
Best of all, the car ride now feel so reassuring and incredibly surefooted.