Erik (aka AlienBOB) has uploaded Slackware packages for KDE 4.5 RC 1 on his KTown repository and now it has been mirrored on UKDW's Repository for local access. Even though there hasn't been any official announcement (which made me think that it was behind schedule), the sources for RC 1 has been available for few days on their FTP Server (i didn't check this). Maybe they are waiting for Monday for an official announcement.
Anyways, KDE 4.5 RC 1 will have a different dependencies compared in Beta 2, so you will have to upgrade several packages in deps/ directory as well.
For you who enjoyed testing KDE packages, this is your chance to test the upcoming KDE 4.5 which is planned to be released on August 2010.
Note: You will need to use Slackware 13.1 and newer in order to use this packages. Please read the instructions on the repository.