A bit more testing:
attacking a realistic 3 squadron, 32 ship combat box of B-17s with the latest build is tough, very tough, as long the the formations stays together. Attack from behind and you're almost certain to get shot down. I found that the only way I could get in more than 1-2 attacks was to attack the formation head on, which seems quite realistic.
If only we could get the bombers to stay in formation while firing back... I'll try Shahdoh's defense script later tonight.