I don't know if there is a workshop figure, but 0.5 mm seems a sensible absolute minimum to me.
I any case, long gone are the days when I pursued HPC. The more volume the better IMHO.....

Plus the drag of rotating webs in close proximity (windage) is reduced.
(I had a batch of alloy mag flange gaskets made a while back. Brilliant as they are re-useable. Is the World of Lambretta ready for such Demonic ideas
)