by theory
It really depends on who can wrest control of the Mid War regions.Between experienced players, Early War almost always exits with USSR anywhere between 0 and -10, although sometimes a strong USSR can push the US to -15 or even autovictory. If the USSR can score Mid War advantageously and/or re-score an Early War region, they can use that advantage to get to autovictory sometime in the Mid War.
If the USSR can't get that autovictory, it usually falls behind by the end of the Mid War, and then the question is whether they can hold onto a -7 lead for Wargames on Turn 8-9. If they can't do that, then their chances of victory in Final Scoring are quite low.
DEFCON throws a wrench in all of this; in general the USSR is a little more vulnerable to DEFCON, whereas the only real threat to the US is Lone Gunman.