Does your KDE Photo Slideshow screensaver run with slow transitions between photos? Buried in the Bug Tracker is this little gem:
Paul Lemmons 2011-12-16
..."I wish I could simply disable all transition effects."...
Add the following line:
EffectsEnabled=false
to the end of the file:
~/.kde/share/config/kslideshow.kssrc
And your wish is granted