The S&P 500 is coming off its best midyear stretch since the 1950s. Now it’s a question of taking some profits or holding for a rally at year-end. - Getty Images/iStock With the S&P 500 on pace for a 16% yearly gain already, investors find themselves at a familiar crossroads: lock in profits while they are hot, or stay greedy and bet on a typical year-end rally that could push stocks to new highs. The S&P 500 SPX just defied one of Wall Street’s most entrenched seasonal clichés — “sell in May and go away ...