U.S. investors have all but tuned out the boldest and best mutual fund stock pickers, leaving billions of dollars on the table for each of the past five years.

Stung by the 2008 financial crisis, mutual fund investors have plunged into low-cost, low-risk passive investments such as index funds, happy to take whatever the market gives them instead of reaching for excess returns.

But the opportunity cost has been enormous.

An easy way to look at it is to compare rival mutual fund titans Vanguard Group, the reigning champion of the index fund, and Fidelity Investments, whose actively managed portfolios have outperformed benchmarks for the past five years.

Vanguard received $75 billion in net flows in 2013 - more than three times any other firm - while Fidelity had only $5 billion in net flows, lagging about half of the 35 largest fund families, according to Morningstar Inc.

"The Vanguard tsunami leaves all of us a smaller player," said Art Steinmetz, who oversees $232 billion in assets as president of OppenheimerFunds. "You can't do it more cheaply than Vanguard with their scale... Year in and year out, they have every day low prices and they don't have to apologize for performance," he said.

The price tag for playing it safe becomes clearer when you drill deeper into the numbers: The average actively managed stock fund at Fidelity has outperformed its benchmark by 1.33 percentage points, net of fees, each year since 2008. That has resulted in $35 billion worth of added value, or outperformance, for Fidelity's investors, said Brian Hogan, president of Fidelity's Equity Group who oversees $750 billion worth of actively managed stock funds.

Hogan holds up Joel Tillinghast, portfolio manager of the $48 billion Fidelity Low-Priced Stock Fund, as one of Fidelity's ultimate active stock pickers. Over the past 24 years, Tillinghast has outperformed his benchmark by 5 percentage points a year after fees.

But investors are not stampeding into Tillinghast's fund to access his returns. In fact, over the past five years, investors have pulled nearly $3 billion from the fund in outflows, according to Lipper Inc, a Thomson Reuters company.

Christopher Philips, a senior investment analyst at Vanguard, said a lot of money managers are trying to move away from the poor marketing image of no skills and high fees by becoming more active. But he also said there's no guarantee portfolio managers with high active share can beat their benchmarks year after year.

"The case for active management is the opportunity to outperform," Philips said, stressing the word opportunity. "But higher costs are there and so is the risk of underperformance."

Ebb Tide

While a bad stock pick can undo any manager, recent academic research reinforces the argument that active management provides benefits to investors in the long-run.

Antti Petajisto, a former Yale University finance professor who now works for BlackRock Inc, concluded that the most active stock pickers in the industry have been able to beat their benchmarks by about 1.26 percent a year after all fees and expenses, according to his results published last year in the Financial Analysts Journal.

Fidelity's Hogan said he believes investors will eventually notice, turning the tide of money flows back in his company's direction. "It would be great to get those flows, but they're a lagging indicator," he said.

Still, executives from Fidelity and other mutual funds acknowledge that a significant hurdle to drawing risk-averse investors into actively managed funds is less about the long-term performance, and more about the short-term volatility that sometimes accompanies stock-picking.

The $1.5 billion CGM Focus Fund, for example, beat the S&P 500 Index last year by 5.22 percentage points with a 37.61 percent return. Run by Ken Heebner, the fund's composition was 97 percent different than its benchmark. But a key volatility measure was nearly 80 percent higher than the S&P 500, according to Morningstar. The takeaway is that investing in Heebner's fund is akin to a roller coaster ride.

Fidelity and OppenheimerFunds have said they want their portfolio managers to pick stocks while keeping a sharp eye on tracking error, which measures the volatility of a portfolio's returns relative to its benchmark.

If done perfectly, an active manager can look different from his benchmark without straying too far from the benchmark's risk profile, said Laton Spahr, portfolio manager of the $2.4 billion Oppenheimer Value Fund.

"With active share you can keep the risk profile of your benchmark, but your returns can be better," Spahr said.