I have no brain to figure out a good RI solve, so instead I just solved for R. As far as I can see, it is most efficient to deplete golds all the way to lead to get the second quicksilver per output, getting a ratio of 69 inputs per 41 products. 
Edit after main stream: I overcooked. No idea how I missed the much simpler ratio of 5 inputs per 3 products, but well, it happens.