What about 350%? (USA)

That number seems to be inaccurate. The Treasury Direct website http://www.treasurydirect.gov/NP/BPDLogin?application=np states that the total U.S. public debt is: 10,943,838,929,434.92 (~11 trillion dollars). The U.S. GDP is close to 14 trillion dollars, making the debt somewhat less than 100%. I'm not sure where that 350% figure comes from.

I think it is debt owned by banks not national debt.

Depends if you spent the money you borrowed on Nukes or Herring :-)