I Agree with powder coating the running boards to match the current rim color. There are wheel treatments you could apply to combat the brake dust, or go with ceramic pads...zero dust from those.

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2005 BMW X5 4.4 Sport Upgrades:

Dinan Cold Air Intake
Dinan Stage II Software
Akebono Euro Cermaic Pads
Brembo Rotors
Titan Silver Metal Gauge Rings
DICE IPOD Module
Hardwired Passport 9500ix Radar/Laser Detector