Well I think Russia did rather well from 1906-1913 in terms of growth so best case is probably the Soviets go for post cold war Chinese styles 'communism' and invite western Europe and US industry to get involved even if it did default on some of its pre war debt, I think this is forgiven quickly and it would still be welcomed back into the international world....
Yeah, no. "Consumer communism" would not be enough to get the west to tolerate the Bolsheviks. The Bolsheviks were scary because they were revolutionaries who advocated overthrowing the entire system the West was built on. Whatever they wanted to replace it with, they'd still be a threat.
What is the absolute best-case scenario for early Soviet industrialization, ignoring internal politics and leadership? What policies or treaties would advance the USSR the absolute most, providing the largest possible industry and prosperity? Ideally, it would have the lowest death toll from famine as well.
Best case scenario in what sense? The best case scenario for getting the most industry by 1941 is different from the best case scenario for getting the most industry by 1955.
If you want the best long-term outcome, then Bukharin's ideas were the closest (so continuing to allow small scale free enterprise and allowing the peasants more freedom to choose what they farmed, how to farm it and the ability to sell their produce coupled with state-led development of heavy industry). There's pretty much no chance that those ideas would have been chosen.
The next best long-term outcome would be the "Trotskyite" path - that is, the Soviet Union being more open to trade in goods and ideas (Stalin forbade Soviet scientists to travel abroad to conferences, which enormously damaged scientific inquiry in the Soviet Union) while collectivizing agriculture and pushing aggressively to build more heavy industry, only starting a couple years earlier than OTL. A surviving Lenin or Zinoviev becoming leader of the party could lead to such an outcome. Starting collectivization early helps enormously, since the peak of the collectivization campaign doesn't coincide with the trough of the Great Depression grain-price collapse AND with a natural drought (starting collectivization late also saves millions of lives - the Soviets OTL really had poor timing on this one).
fasquardon