That's not how max old space works I'm afraid. All it does it provide a hint to the V8 engine to do GC at that level of stack use. It doesn't change the total amount of memory available to Node.js.
That in itself will help of course but only in very specific circumstances which is why I never both with it and haven't since I stopped using my original Pi1 - not sure it really helped even then.
Earlier GC will tend to keep a little more stack space available to node.js which is why it can delay crashes due to out of stack problems but that is all it does as far as I am aware.
