You can write a separate Comparator to compare your object which will have the capability to sort in reverse(just opposite logic what you have implemented) instead of implementing compareTo method in our object(while I can see that your class doesn't implement Comparable interface).
In that way you will be able to directly get the reversely sorted Set and you can change the logic easily anytime you want or can use many different comparators at the different places.
For 1000-10000 using TreeSet is a good option with Compartors.