Stratbombers and Dark Skies are so flexible and effective, that buying up to 6 is optimal play. Strategic bombing is a bit too powerful OOB because Russia has little defense. But on top of that, the 6 range and cheap cost makes them a bit overpowered–they are one of the few units that can consistently reach some interesting target the turn after they are built.
After almost 200 games in the last 3 years, I need to try new things.