Sometimes an eight-cylinder

Cadillac

moves along the curves just as swiftly as a fiery new Miata,

Fidelity

proves.

The $27 billion

(FDGRX) - Get Report

Fidelity Growth Company fund has been stepping on the gas pedal, racking up a 37.8% return so far this year. That's on top of a 79.5% gain in 1999. The feat gives it the best performance so far this year among the 25 biggest mutual funds, according to

Lipper

.

Funds of such heft aren't typically performance standouts. In fact, within Fidelity's own shop, the $45.1 billion

(FCNTX) - Get Report

Contrafund and the $44.9 billion

(FGRIX) - Get Report

Growth & Income have been lumbering along, turning in returns of 4% and negative 4.7%, respectively. The biggest of them all, the $100 billion

(FMAGX) - Get Report

Magellan fund, is off by 0.7% through March 3.

What's keeping this fund so nimble -- despite almost 300 names in the portfolio -- is manager Steven Wymer's healthy appetite for technology stocks and a timely move last year out of drug stocks in favor of biotech.

``Usually you see this type of performance when a guy or gal has two dozen positions,'' says Eric Kobren, executive editor of the

Fidelity Insight

newsletter in Boston. ``But he's been able to do it with diversification.''

True, other funds enjoying similar returns are considerably slimmer and therefore more agile. For example, the $601 million

(JAGLX) - Get Report

Janus Global Life Sciences fund, up 75.7% year to date, has just 61 holdings. The $1.8 billion

(TVFQX)

Firsthand Technology Value fund, up 53.9%, has 63 names.

Since taking over the fund in 1997, Wymer has steadily been moving down the market-cap spectrum, finding winners in small- and mid-cap names, which represent about 40% of the holdings, according to fund tracker

Morningstar

. The fund's average market cap was roughly $12 billion in November. A year prior, that average was $14 billion.

Instead of benchmarking itself against the

S&P 500

, an index full of large-company stocks including value laggards, Fidelity uses the much smaller-cap and more volatile

Russell 3000

. Good thing -- the Russell 3000 index is down just 2.6% this year, about half the 5.3% loss posted by the S&P 500.

A Fidelity spokeswoman insists that the stock selection hardly changed when the company switched its benchmark at the beginning of 1999. ``It was more reflective of the way the fund was already managed,'' she says.

That may be so, but performance shot up dramatically in 1999, and Growth Company turned its back on two years of lagging its peers. But that's not to say that Growth Company has been buying in lockstep to the Russell. It's seen its share of adept stock picking.

Not surprisingly, as Fidelity moved down the capitalization spectrum, its exposure to some of today's technology highfliers soared, particularly chipmakers and networking stocks -- this market's darlings. It went from just a 26.8% weighting in the tech sector -- mirroring the S&P 500 at the time -- to a 45% stake today.

Growth Company has 2.4% tucked away in fiber-optics maker

JDS Uniphase

(JDSU)

, up 73.8% year to date. Another 2.8% resides in

National Semiconductor

(NSM)

, up 80.87%. And Wymer has taken on network storage provider,

Network Appliance

(NTAP) - Get Report

, up 140.71% year to date. (No. 1 holding

Microsoft

(MSFT) - Get Report

is down 17.7% for the year, though.)

``With these stocks, Wyman basically hit a grand slam,'' Kobren says.

Wymer, an 11-year Fidelity veteran (he also ran Dividend Growth and two Select sector funds), also has a fondness for biotech, and in his annual report he touts

MedImmune

(MEDI)

, the vaccine maker, as a particularly good buy. That stock is up 22% year to date. In the same report, Wymer is especially sanguine about human genome work and new drug therapies. He trimmed the fund's overall health care exposure from November to December, cutting back on large-cap pharmaceuticals. But he's kept names like

Genentech

(DNA)

, up 68.3%, and

Human Genome Sciences

(HGSI)

, up 183%. Biotech makes up about 7% of the fund.

``This is one of the few funds that was up in January,'' notes Diane Finnerty, an investment adviser with

Ventur Asset Management

in Locust Valley, N.Y., who doesn't own the fund. ``He made a 4% return in a down market.''

Though Growth Company is riding the wave of good performance now, that strategy hasn't always proved a good bet. The fund's penchant for smaller stocks led to underperformance in 1998 and 1997. In fact, it fell behind its peers for most of the five years under Wyman and previous managers Larry Greenberg and Bob Stansky, who later took over Magellan.

``It has a lot more exposure to mid-caps and small-caps than some of its peers,'' says Scott Cooley, a senior analyst with Morningstar. ``And it's paid the price for that. But last year, it paid to have exposure there.''