Soviet Economic Growth since 1928. The Alternative Statistics of G.I. Khanin. See Table I. Personally I'm of the opinion that Khanin's numbers are probably the best there are (not all would agree). Maddison's numbers are roughly the same as CIA's numbers. I've also already created an image based on that data: 

  

 As can be seen, the official Soviet statistics *always* exaggerated growth, sometimes by a buttload. The CIA generally overestimated actual growth (because 1) they based their estimates on official data and 2) they also wanted to justify higher budgets for themselves and making the Soviet economy a bigger threat served that purpose) but not as much. However, for the purposes of this discussion, it turns out that for the 1950-1960 period, the CIA actually *underestimated* Soviet growth. At the end of the day, it is true that between 1950 (probably a little earlier) and 1970 Soviet economic growth was pretty high. This had three causes. One, it was the rebuilding of the capital stock destroyed in WWII. This almost always happens after wars if political stability is present. Two, high rates of saving and capital accumulation. In a market economy the national saving rate is determined by individuals. In a planned economy it is determined by the state (you just pay people less). So it's much easier to raise savings rate (and hence, temporarily, the growth rate) in a planned economy, at the cost of consumption. Three, there was a substantial reallocation of labor from the low productivity agriculture to higher productivity urban sector. This is a general "one time payoff" that one frequently observes in many developing countries.