All risks is about €1 - €1.50 per hundred euro value, depending on insurer. At €11k, you would be paying €110/€165 per annum for the ring alone. if Hib are €1.50 per hundred, then €160 is right.
Given the value of the ring, I would be reluctant not to have it insured. however, bear in mind that the jewellers often give valuations for a higher figure than what you bought it for. This to give some form of psychological boost to purchaser who feels that they have got a great deal, ie buy ring for €8K with valuation of €11k, could lead you to thing that you have got a bargain.
I would sugest that you insure for the true purchase price and even perhaps a little less as i am quite sure if you went into shop toomorrow to buy an €11K ring, there would be some discount on the list price.