Ok, regarding multiple monitor desktop backgrounds on KDE (Currently running F18 / KDE 4.9.5):

1) Is it possible to span dual monitors with a single image in KDE? As far as I knew, it was not possible in KDE 4.2, and I do not know if that has changed since.

2) (My main question) - I have taken 16 3840x1080 images, split them into 1920x1080 images titled (imaginatively) Wallpaper-(x)a and Wallpaper-(x)b. I have them all of A in a folder, and all of B in a folder.

On screen 1, I have set slideshow to folder A, and on screen 2 I have set slideshow to folder B.

Ideally, I would like to stop the randomization of the wallpapers, and have A and B match up.

Is this currently possible?

With regards to spanning a single image over multiple monitors: there has been no change here, this is not possible. To simulate the effect, you could split the image in two and set the appropriate halves on each screen however.

With regards to Randomization - it appears that part of the infrastructure to support non-randomization is in place in the slideshow wallpaper, but it is incomplete (it does not read any configuration, nor does it have any user interface. If you are up to compiling the wallpaper code, then it may be possible for you to get a non-randomizing version.