you could also look at how fast germany collapsed in the east after d-day,because it was way out of proportion to the retreats they had made pre-d-day. They collapsed in the east after d-day.
either way i think that if the russians had attacked germany first, and tried to invade as the above poster said they would, they would have been smashed.
they wouldnt have the russian winter, which realy has saved them in countless wars, and they would be crushed.
we know this, napoleonic wars, every battle outside russia pre 1812 they lost to france, in the russian campaign 1812-1813 they lost until the winter.
russia realy has a terrible military history, they have been saved countless times by their enemies under-estimating the winter.
this also happened with germany, they failed to take moscow because of the winter freeze.