DrawMeshInstancedIndirect vd DrawMeshInstanced performance

Hi there,
Do shadows in forward rendering path break DrawMeshInstancedIndirect resulting in same or worse performance than DrawMeshInstanced under same conditions (ie. same number of instances, scene setup, lighting, shader logic..)?
I have a test scene where DrawMeshInstancedIndirect improves performance considerably (not shadows). However as long as shadows are enabled, the performance gain is lost (almost identical performance using both APIs).
p. s. scene uses around 90K spheres, forward rendering path, 4 shadow cascades.
Regards