For the Allies to win, the Soviet counterattacks must be focused – and lucky! Build/borrow as many fighters as you can. Also I advise NOT strategic bombing. I cannot see how the high risk of aircraft loss is worth the gain of turning six German IPCs into ash. Gimme a break. Take out a couple of Wehrmacht infantry, and strafe & bomb Panzer divisions from the safety of a combined air-ground attack, and you can wipe out dozens of IPC value, with zero threat to your expensive air wings. Much better deal every time.
Meanwhile, the order of the day for the Yanks and Brits is to correctly manage the balance of transports, destroyers & troops they’ll need for D-Day. Simplify: Tan boats will haul tan troops, green will haul green. See if you can steal a forward fighter base, maybe best in Norway.