At first I think nobody will scroll the list which contains 6000 elements to find proper one. I would rather expect that the user will enter some more caracters. So maybe some solution like
- option 100
- First 100 Options shown
will suit your needs?
And the second - which scope your bean has? If request - db call will occurs on every request. And it also not looks like optimal solution.
In general all the SB component functionality is to call your suggestion method and ask for some list of suggestions. So almost all the performance tuning should be adressed to your object.