19"/20" Rims: Bad Ride Quality?

[X5audi]

Our X5 was delivered to the dealer on Wednesday, and we have yet to pick it up (not enough time!). So that leaves me room to think about the rims. We did not get the Sport Package on our 4.8i, and I'm wondering how bad the ride quality would be if we bought the 19s or 20s available on the 4.8i Sport Package by themselves.

Or rather, how different. It has a plush ride without them, as did the one we drove last month. (Yes, it was delivered that quickly! Crazy!) How rough do the 19s make it? The 20s? I'm definitely wondering if either of them are worth buying, because they simply look so much better than the 18s.

Thanks for any replies.