If i was cataloguing it for auction i would want a lower estimate, although i'd hope it would reach the figure they've given.
A couple of years ago i catalogued an ivory plaque by this artist / sculptor
http://collections.vam.ac.uk/item/O89694/oliver-cromwell-1599-1658-relief-van-der-hagen/Very few are sold at auction and the subject was unknown, unlike his carvings of Cromwell, Elisabeth I etc. I managed to get it into the catalogue in the hundreds...it fetched £6,000 ( more than £7,000 when adding commission )
It can be risky but i usually find that the more people who think they've a chance, the higher the price. Get the people in the rooms, get the internet bidders, get the people on the phones. Smack a big price on something and usually the bidders don't register their interest.
Contact the museum
Contact that website i've linked to, ask them how much they sold that dagger for, and if they reply know that yours is better.