What is the expected rate of return in the latter case? You're promising 3-6% growth in one case and promising the potential to go up or down 15%. Looking across a one year timeframe the stock market could, in the extreme go up ca. 60% or down as much as 50% (based on history). But the expected annual return based on historical averages is 8-9%.

Given a long enough timeframe, I'd gladly take expectation of 8-9% returns while risking extreme short-term fluctuations -- even more extreme than your +/- 15% scenario.

Back to your question... Is there an equal likelihood of +/- 15% (in which case we might expect returns to average 0%)? Or something else?