On Monday, the bull market in U.S. stocks enters its sixth year. Since World War II, only three of the past bull markets that made it to the fifth year lasted for at least a sixth year. That’s not a lot of history to go by, but the super-strength of two of those bull streaks makes one wonder, “what if…?”

To see what history could tell us about the future, MarketWatch’s design team projected where the S&P 500 SPX   would end if it repeated the sixth-year performance of the 1950s bull market, the 1980s bull market, and the 1990s bull market.

Another 38% gain, along the lines of the the 1950s run, would bring the index to 2,600 from  its Friday close of 1,878.

Of course, a colossal thud along the lines of the 1980s bull market could also occur. Indeed, if the five-year bull market that peaked out in 2007 does a repeat in the next 12 months, investors would be looking at a 42% spiral to 1,092.