From BCWipe's options:
-n sec Wait sec seconds between wiping passes. (NAS mode) ***

*** - modern enterprise level storage systems (NAS, disk arrays etc.)
employ powerful caches. To avoid undesirable caching effects
use this option to insert delay between wiping passes.
Is there any recommended value for this? Should I consider my normal 80GB hd a "modern enterprise level storage system" and use this option?