Dear Shyam, I think you are doing well at .9 mm. Of course it is
relative to where the thinness is in the piece. I think trying it
would be to your advantage, but structurally thin cast metal is soft,
so bear that in mind. You probably can run circles around me, but it
sounds to me like you have pushed well into the thinnest possible.
You can certainly do better with a centrifugal caster than vacuum,
but I think you may already be at maximum thinness in general.