So keep in mind that difficulty is relative to what you want to make difficult in this particular game, and that tuning those Ob knobs is a big part of setting up the game expectations.
And I stand by what I said. Ob 1-3, maybe 1-4, should be most tests for most games, at least until everyone’s always doing crazy stuff after a year or more of consistent play and increasing stats. There will be harder tests, of course, but they should stand out as the exception, not the rule. Because those harder tests are hard and should hurt.