What better evidence could we have than tests carried out with the round we're discussing, against steel plates such as the ones carried on tanks of the day? The only thing that can be said to depreciate the value of actual tests is that various countries used test plates with different BHN values and different definitions of what "penetration" was. In any case, these actual tests are bound to be far more true (because they are what actually happened) than mere calculations.
Well given the hardness of Russian armor, its probably fair to conclude the armor they tested against would have been hard as well. That could have skewed the results a bit. PS, I think the battlefront mod has died or something, still haven't gotten permission in an e-mail to post on the forums yet...