As small-cap mutual funds outperform the broad market, $2.2 billion Oppenheimer Discovery Fund has topped its small-cap growth peers tracked by Morningstar Inc. and the S&P 500, both year to date and over the past year. Over the 12 months going into Tuesday, Discovery racked up a 10.04% gain, beating 86% of the stock mutual funds that are its direct rivals, which averaged 9.12%. The big-cap bogey gained 7.10%.