By discussing the Soviets winning the Cold War, I presume that the Cold War never grows hot leading to a nuclear showdown between the two sides. Given that condition, I think you would need an ASB to produce a Soviet victory. Their economy, in spite of certain tour de forces in military technology, was just too primitive compared to that of the West. Their rate of technological innovation was much, much slower. Their system hampered the necessary creativity. Excessive secrecy meant that scientists working on different projects couldn't learn from each other. By the 1970s Soviet society had become cynical. Their allies were economic basket cases, disloyal, and cost more money than they were worth. Anyone smart enough to try to tackle these problems would realize that the answer was to junk the system, not strive for an unachievable victory over the U.S. To quote Gorbachov, the USSR needed to become a "normal" society. But insofar as it became a normal society, the Cold War would become meaningless--or rather, just be transformed into the typical economic and diplomatic competition between nations.