Large-cap stock mutual funds trail small- and midcap funds in performance the past 10 years. That’s nothing unusual as small-cap stocks tend to outperform in the long term. A $10,000 investment in the average large-cap mutual fund on June 30, 2005, would have grown to $21,968 by July 21 this year, trailing midcap funds’ $24,997, small-cap funds’ $24,046 and the S&P 500’s $21,976, according to Morningstar Inc. data.