Thanks, I’m glad you’re receptive to the idea 
I’m not sure how to establish an acceptable lower bound for the tolerances. The upper bound should be the optimum that can possibly be achieved under ideal conditions given the current nodes and their diversity across the relevant characteristics. I think a sensible lower bound would need to be calculated by taking a percentage of random nodes out of action (simulating failure conditions) and then calculating the optimum under those conditions.
My understanding is that the tooling currently isn’t there for answering these questions in a rigerous way. I’m hoping to help get there with the optimisation tooling I’ve been working on. Until that’s further along, I guess the best option is to feel our way through the problem.
Perhaps something to discuss further over the next few weeks, based on what seems feasible in practise?