Jarv, I think recognition of when your developer is hitting the sweet spot in terms of concentration, temp, OB and stray debris like dog hair and insects is more important than chasing f-stops. I find test strips to be particularly non-instructive, even more so as they have a dry-down of their own. Not to say f-stop printing in lith is not useful; it gives a wide range of control. But if your developer is well-seasoned you can throw just about anything in there and get something good back.