"Go To Board" very slow

The "Go To Board" link on an issue takes a long time, and sometimes times out. We have 650K issues, a few hundred boards and the issues are often on 3 to 5 boards. The boards generally only have a few hundred issues in them.

Does the underlying code for GHGoToBoard.jspa simply examine all boards and see if the issue id is in each board's filter? If so, I think there is a scaling problem coming up.