I'll give you my impressions based on RD Sporst only (I have no experience with the H&R on the M3).
The driveway to my house is very steep so I will list some cars that scrape on it and some that dont to give you an idea how low it is:
E90 M3 with 18's (RD Sport): No scraping
Viper GTS with stock wheels (not lowered): scrapes slightly
Porsche 993 with 18's (lowered on H&R): scraped slightly
Acura NSX on 17f/18r's (lowered on Intrax): scraped
Stock C6 Corvette: Scrapes the plastic flap
On speedbumps I have yet to scrape. If you have EDC I would put it on the stiffest setting when going over speedbumps or steep inclines. The main thing that causes to bottom out is when you dont take your time going over the bump and the spring compress too much...TAKE YOUR TIME GOING OVER A BUMP OR GOING INTO A STEEP DRIVEWAY.