BOSTON (Reuters) - Hedge fund White Elm Capital is returning money to outside clients at the end of the year, ending a 12-year run of picking stocks for pensions, endowments and wealthy families, its founder, Matthew Iorio, wrote in a letter on Friday. Iorio, whose fund is having one of its best years ever with a nearly 30% gain after fees, said it was the right time to end. He called the decision "very difficult" but said he was "happy to be returning capital when we are performing at the top of our game."