I'm using linear depth, it's a big help.
Bias doesn't work so well with backfaces though, here's a with + without, note the spilling of shadow at the top of the box now:
Is this your experience too?
How do you do the slope scale bias? Previous I have done something like this
bias = a + b / L
where L is the normal dotted with the light direction, i.e. from the diffuse lighting equation.
Front face shadow casting doesn't have the problem illustrated in the screenshots because it's hidden underneath the object where you can't see it, but choosing the bias is a horrible nightmare. A bias that works well from one angle doesn't work for another angle, and the bigger the PCF tap (in terms of area in texels covered) the bigger the bias has to be too. It's easy to end up with a bias that is too small from some angles (shadow acne) and too large from other angles (appearance of levitation). I wonder if lispsm is really worth it, for all the complications it causes with this kind of thing.