If you have soft shadows enabled on only one light(light-lab), it is the same as turning on premium FX. Conical lights are worse than radial lights. If you use premeium FX, please belive me, you don't need 128 or even 64 rays per pixel, unless your render is the size of a dinner table. A high haze setting is often a good subsitute for a volumetric FX. EXPERIMENT!