Seven years ago to the day, a new vehicle for gold launched straight into stardom and became the dominant means by which investors have gained exposure to the best-performing asset class of the last decade: gold.

The SPDR Gold Trust (NYSE: GLD) -- known colloquially as "the GLD" -- has seen its reported gold holdings explode from just 0.26 million ounces at inception, to a meaningful stash of 41.86 million ounces seven years later. Thanks to the explosion in the price of gold that corresponded with its rise in popularity, the fund's net asset value grew from $115 million to a whopping $72.2 billion. The GLD, then, is worth some 59% more than Goldman Sachs (NYSE: GS)!

With 41.46 million ounces (1,289.46 tonnes) in reported holdings, the GLD lays claim to more gold bullion than the combined (reported) sovereign holdings of India, Saudi Arabia, and the United Kingdom combined! The holdings equate to nearly one-half of all the gold mined in the world during 2010.The fund has further to climb, however, before matching the 140 million ounces of reserves held by the world's largest gold miner: Barrick Gold (NYSE: ABX).

Altering the landscape for gold investment
Although several exchange-traded bullion proxies were available prior to the launch of the GLD, no other vehicle has come close to capturing the attention -- nor the market share -- that the SPDR Gold Trust has commanded over recent years. The reported holdings of the iShares Gold Trust (NYSE: IAU), at just 5.26 million ounces, simply do not compare. When billionaire investors from John Paulson to George Soros go for the gold, they go for the GLD.

Before these sorts of bullion proxies hit the stage, gold investors typically took possession of physical bullion and held onto the metal for the very long term. Between transportation and storage costs, the asset did not lend itself well to the whims of short-term traders, with futures markets offering essentially the sole exception. With the advent of the GLD and similar vehicles, short-term speculators and institutional investors alike now have a compelling niche at their disposal that lies somewhere in the void between actual physical possession and leveraged exposure to futures.

As the vehicle increases in scale, so does the imperative for gold investors to track the trust's data for emerging trends in investment demand for gold in the Western world. For example, John Paulson reportedly liquidated approximately one-third of his hedge fund's GLD holdings during the third quarter of 2011. I believe the sales likely stem from a rash of redemptions by clients in the wake of a couple of very rough quarters for the fund, and gold's strong trailing performance makes that holding an obvious target for strategic liquidation. Paulson reportedly sold 11.2 million shares of the GLD during the quarter, or the equivalent of about 1.1 million ounces of gold. A liquidation of that scale is certain to have an effect on gold price. After all, for all the attention it receives, gold remains a surprisingly minuscule market as compared with other asset classes. As gold continues to rise in price and popularity over the years to come -- a scenario that I consider a foregone conclusion -- the exceptional liquidity provided by the GLD will likely remain a conduit for substantial volatility.

Fortunately for gold investors, an incredible surge in central bank purchases of gold during the third quarter served to underpin the gold price in the face of a rallying U.S. dollar and the spate of forced hedge fund liquidations as bullish bets turned sour over the summer. Central banks added a phenomenal 148.4 tonnes of gold during the third quarter, representing a 123% sequential increase over the 66.5 tonnes purchased during the second quarter, and more than 6.5 times the prior-year mark of 22.6 tonnes. The identity of many of those buyers remains a mystery, though I suspect China may be overdue for another public restatement of its official gold holdings. In any event, those 4.77 million ounces in central bank purchases represent the strong bullish hand of willing buyers on the other end of those sudden liquidations by Paulson and others. With central bank gold purchases forecast to continue in earnest, the outlook for gold remains, well ... golden.

A golden record of performance
One would have to have dug pretty deep into a bag of tricks to outperform the GLD over the past seven years of a lost decade for stocks. Thank goodness for Apple (Nasdaq: AAPL), which -- as a result of its broad-based appeal -- likely helped droves of investors to reduce that twinge of regret that gnaws at the heels of those who have eschewed gold exposure thus far. Google (NYSE: GOOG) forged a rather legendary trajectory following its IPO mere months before the launch of the GLD, but after today you can search for "GLD outperforms Google," and you'll end up right back here where you can consider the following chart:

SPDR Gold Trust ETF Stock Chart

SPDR Gold Trust ETF Stock Chart by YCharts

Over the seven years since the SPDR Gold Trust entered the fray, the trust has edged out even the rather epic performances logged by celebrated large-cap stocks Google and McDonald's (NYSE: MCD).

I find it interesting to note here, though, that a lesser-known and far-smaller bullion proxy has outperformed even the mighty GLD. I refer to Central Fund of Canada (AMEX: CEF), which I have consistently touted as my own preferred investment vehicle for precious-metals bullion exposure. The fund has been around since 1961, which makes this year, of all things, its golden anniversary. Central Fund of Canada also offers investors a critical promise of "unencumbered" bullion within its prospectus that is not explicitly stated within those of many popular alternatives. Moreover, this vehicle offers a unique mix of exposure to gold and silver, which I believe will prove a driver of even greater outperformance going forward. I encourage Fools to consider billionaire investor Eric Sprott's forecast that "silver is the investment of this decade as gold was the investment of the last decade." For those reasons, I believe Central Fund of Canada remains the bullion proxy of choice for discerning precious-metal investors.

But the greatest outperformers of all, I maintain, will be the miners of gold and silver. After a terrible year thus far in 2011, the mining equities are ludicrously undervalued and poised for substantial outperformance of bullion. I believe bullion exposure remains a core component of any well-structured strategy for precious-metals investment, but at this juncture I recommend an enhanced relative allocation to miners over bullion. I think Primero Mining (NYSE: PPP) is about the greatest gold stock in the world, and my top pick for 2011 -- AuRico Gold (NYSE: AUQ) -- remains a phenomenal value following a pair of hugely transformative acquisitions.

To mark the occasion of the SPDR Gold Trust's seven-year anniversary, take a moment to share with your fellow readers your strategy and/or selections for precious metal investment to profit from the remaining years of this powerful bull market. Whatever your thoughts on gold bullion or gold miners as an investment, Foolish minds want to know. Please find the comments section below.