I've been using Opera for many years and have never used a repo package for it. I just download Other/StaticRPM, Static QT package, Download this package in TAR.GZ format. Then I unpack it into its own directory, su to root, and run the Install.sh script. I accept the defaults and run ldconfig after the installation is complete.
The Slackware package for Slackware 11 or 12 would probably work, too.