Hey Ant, when I used to CNC cut moulds for the automotive industry, we would lace cut the cavity with very small step overs like .0005 in 4 diffrent directions, steping down Z axis a little also, almost the same and running the spindle at a high rpm using a small carbide ball nose mill, this would save almost 200 hrs of hand polishing, we would just let the cnc mill run all week end. Dont know if you have a CNC mill but just thought I would mention it to ya.
Cheers