PCF 8 gives very bad results indeed on your card…
I have this
Note that the pattern will always be worst on solid colored geometries than on textured ones.
you can aleviate those patterns to some extend by playing with the number of shadow maps (default is 3 in the test)
and by reducing the lambda values (default is 0.55 in the test)
Here in this shot, there is 4 x 1024 shadow maps and lambda is 0.3 (still PCF8).
You can see that the transition is a lot smoother.
I recommand to use PCFPOISSON as it’s a lot faster and gives result almost as smooth as PCF8.
In case you wonder, and just to expalin what Lambda does :
It defines how the shadow map are distributed in the camera frustum. Labda goes from 0 to 1. With a low value, you’ll have more definition on the first split (the shadow map clostest to the camera) but lower definition on farthest splits.
That’s because the first shadow map will cover a smaller area than the others.
The draw back is that the lower lambda is, the more obvious will be the transition between the splits.
You can try to play with it to see the difference.