Note Stalin was unlikely to attack before 1942 at the earliest: he'd be looking for the moment of maximum advantage, and the Soviet military modernization, restructuring of the army, etc. was still under way in OTL when Germany attacked. As long as Hitler didn't go to full mobilization of resources (which he didn't do OTL until 1942, when it became clear the war in the east wasn't going to end quickly) time is on Stalin's side.
Bruce
As far as I understand, this is mostly a myth - the Reich did have full war economy going from the start, but they twice changed their priorities, which caused the spike in produciton numbers to be delayed to 1944.
First time was after the fall of France, when priorites changed from land forces to prioritize aircraft, submarines and other assets useful for fighting Britain, and then again at some point during the war in the east (early 1942?) back again to tanks and guns. The "Totaler Krieg" thingey after Stalingrad was mostly propaganda.
Source is Tozee's "The wages of destruction"