How much shim is based on the density of air. And the density of air is base on altitude;barometric pressure;weather. More close to sea level you need more shims. When atmospheric depression coming you may need to take some shims off. Sometime you may run 0.4mm in the day but 0.5mm in the night. Air temperature also has effect on the air density....etc. There is no final answer. You need to try different setting yourself.
When the shim setting is too many(low compression),the engine will get bogged down in low end. When the shim setting is too less(high compression),the plug's coil will be pushed in then burnt.