BOSTON (Reuters) - Activist investors have been outperforming their peers and the broader market this year by pushing for board-room changes rather than dramatic business overhauls, breakups or mergers, according to performance data and industry sources. The average activist hedge fund returned 8.76% in the first quarter, ahead of the broader hedge-fund industry's 6% gain and a 5.8% rise in the S&P 500 stock market index, Hedge Fund Research data show.