you forget that ostheer teching is expensive, soviets need not to tech any further than at nades and at guns and than safe up for call in t34-85s. Good luck with getting your 2 panthers, they will cost you just as much as 4 t34-85s 
I'm rather positive that ost teching doesn't cost 500+ fuel as alex is stubbornly trying to show for some defying any logic and common sense reason.
Also why would you want panther against 34/85?
Have you not read the stug changes? StuG have just become 2nd if not 1st most cost effective TD in game.
Spammable, like alex posts, cheap like tea makers arguments, firepower of SU-85.
Name me ONE reason why you would not want as many of them around your tiger as possible?