I guess the tricky part here is defining the term "mostly written". My mistake for introducing it (and of course the tautological 'don't prematurely optimize').

I guess the tricky part here is defining the term "mostly written". My mistake for introducing it (and of course the tautological 'don't prematurely optimize'). Agreed, you should measure as soon as you can and it's best to be building and measuring, not guessing where your bottlenecks are up front.