How To Turn $100,000 Into $5.1 Million In 7 Months

July wound up as the second straight down month of the year for most S&P 500 investors. But some stocks rallied anyway. If you invested $100,000 in January in the top-performing stock in the S&P 500 at the time and reinvested that in each month's top performer, including computer chipmaker Cognizant (CTSH) in July, you'd have $5.1 million now, says…