Thanks. The couple of used X3 3.5's I am looking at right now both come with M sport packages, one is fitted with Sport suspension and the other with Standard suspension. None of them have DDC, which you do. They both have 19 inch wheels which should help as far as not being too harsh compared to your 20 inch wheels.
I have a bad feeling that the ride with DDC and H&R's is completely different than the ride for a car without DDC, and H&R's.
Here's a guy like you with DDC, who put on H&R's, and seems pretty happy:
http://x3.xbimmers.com/forums/showthread.php?t=780009
Whereas here's a guy without DDC who put on H&R's, and hated them after just a few days:
http://x3.xbimmers.com/forums/showthread.php?t=829676