I’m going Barbarossa with Germany then my objective is to take Moscow on G5, before the Siberian units can make it back. The earliest the first 6 can get there is R6, then the rest on R7.
On the other hand those units (when retreated) could be useful if Russia can stall Germany a turn or 2, or they could be useful in helping out China or fighting Jap units coming out of China.
It’s an interesting question whether sitting in Korea and inviting the Japs to attack is worth it. It’s +3 for each turn you hold Korea, plus the headache faced by Japan with USA being to land aircraft there, plus whatever kills those infantry/aa can inflict if/when Japan attacks.