Doh. Off by one! Yes. T-34. There was a recent analysis by the DoD, finding that the logistic costs of modern MBTs scale by the fifth power of their weight. This is a big problem with state of the art modern tanks. Right now, reactive armor is good enough to stymie 105mm and 120mm guns in battle conditions. However, making tanks heavy enough to support 140mm and larger guns looks like it will make them prohibitively expensive.