The Dow closed above 14,000 Friday for the first time in more than five years. It was just a number on a board, but it was enough to raise the hopes of some investors and cause others concern about an overheated market. The Dow, an index that is traditionally considered a benchmark for how the entire market is faring, had been rising fairly steadily for about a month. On Friday, strong auto sales and optimism about US job growth pushed it over the mark. Professional investors usually pay more heed to the S&P ­index, which tracks 500 companies vs. the Dow’s 30. After the Dow hit its all-time record in 2007, it fell almost steadily for over a year.