Having had the stock, Superdragger and Nur-Spec, hopefully I can give you some valuable advice.
On noise levels, out of 10:
Stock - 1
Superdragger - 5
Nur Spec - 7
Nur Spec single de-cat - 8
Nur Spec double de-cat - 9
Which is equal to:
Superdragger after 6 months with multiple holes - 9!
Essentially, AFAIK, the superdragger is mild steel apart from the back box and so with a bit of salt on the roads is as about as useful as a colinder in trying to get exhaust fumes out the back box.
The Nur-Spec is stainless steel throughout so its longevity is far superior.
My HKS did not hang lower than the stock exhaust (apart from larger back box).
My Nur-Spec gives much less clearance than the stock exhaust, but even lowered I have no probs with speed bumps.
Hope that helps...