<A target="_blank" href="http://blog.darrenduke.net/darren/ddbz.nsf/dx/8.5.1-fp3-if1-is-available-togther-with-the-fix-list.htm">Darren Duke has posted a link to Fix Central so you can get the Interim Fix</A> to resolve the Domino 8.5.1 performance issues during authentication noted in Technote 1433721.