This is not the calculation being made. Using your numbers, experimenting on little girls needs to be at least 1.001 times as effective as experimenting on chimpanzees or mice to be worthwhile (because then you save an extra thousand lives for your thousand girls sacrificed.)

Well, given that more then 1 in 1000 drugs that look promising in animals fail human trials, I'd say that is a ridiculously low bar to pass.