When it comes to long-term performance, small-cap mutual funds are the big man on campus, and large-cap funds are the weaklings. A $10,000 investment in the average small-cap fund on Sept. 30, 1999, would have grown to $38,010 by Oct. 10 this year. The same investment in large-cap funds would have grown to just $17,793, according to Morningstar Inc. data.