Good discussion. In my playgroup, NO’s off/Dardanelles closed/escort & interceptor allowed/tech allowed (but rarely used)/6-12 bid to allies (typically +2inf on eastern front, +1inf in Egypt, +1 inf in Yunan) seems to provide a fairly balanced game.
When we played with NOs on, the ability of the axis to couple their starting hardware advantage with near economic parity by round 2 or 3 (before the US is even “in the game”) always resulted in axis win. We didn’t take the time to figure out what the bid for the allies needs to be to have a balanced game with NOs on but I suspect it might be between 25-30 IPCs. Of course, our predictable play might be the actual issue!