Amazon.com's $920 million purchase of online shoe retailer Zappos marks yet another win for Sequoia Capital, the venerable Silicon Valley venture capital firm that's rung up big payouts over the years with Google, PayPal and YouTube.

But just how much did Sequoia -- which reportedly held 10 percent of Zappos -- and the other investors make? Well, that's a tad difficult to calculate without knowing the exact terms of the venture deals. Zappos reportedly raised about $45 million over the past decade -- including a $15 million round four years ago.

That means the company sold for 20 times the money invested -- a very good outcome by most measures.

By comparison, one of the larger payouts last year of a Seattle company (sorry, we just haven't had many noteworthy M&A exits this year in the NW) was Microsoft's $115 million purchase of online travel site Farecast.The Seattle startup had raised about $20 million prior to the sale, meaning it returned about five times the amount invested.

So, a side-by-side comparison looks like this:

Farecast -- $20 million invested -- $115 million exit.

Zappos -- $45 million invested -- $920 million exit.

Of course, deals can vary quite a bit based on the terms (cash versus stock), milestone payouts, liquidation preferences of VCs and other factors. 

In fact, The Wall Street Journal's Venture Capital Dispatch blog figures that despite the big price tag Sequoia is not poised to make as much money as it did on some of the other high-profile Internet deals of the past.

In fact, at $920 million -- excluding liquidation preferences -- Sequoia's gross payout would be roughly $92 million.

The key caveat in the above statement is the liquidation preference, a common practice that venture firms use to make sure that they can cash out before other investors sometimes at much higher returns.

PEHub reports -- citing an unnamed Zappos shareholder -- that Sequoia had negotiated a 3x or 3.5x liquidation preference when it came in as a late-stage investor. That's extremely high, and would lead to much larger profits for the firm.

And -- as PEHub's Alexander Haislip writes -- it may have pushed Sequoia's Michael Moritz to lobby more for an acquisition. Haislip also indicates that there may have been tension over the decision to sell between Moritz and Zappos CEO Tony Hsieh.

We've put a request into Zappos to get more details on what motivated the sale and other factors.

Of course, there's also talk of why a profitable company like Zappos -- known for its quirky culture and more than $1 billion in annual revenue -- wouldn't test the waters with an IPO.

That's a riskier game than taking stock in a known entity like Amazon.

And going public could potentially have a larger impact on a company's culture than operating quietly as a unit in the corner of one of the world's largest online retail stores.

In fact, Zappos CEO Tony Hsieh addressed that issue today in his letter to employees:

"We plan to continue to run Zappos the way we have always run Zappos -- continuing to do what we believe is best for our brand, our culture, and our business," he wrote "From a practical point of view, it will be as if we are switching out our current shareholders and board of directors for a new one, even though the technical legal structure may be different."

Stay tuned to TechFlash for more reports on the Zappos deal from @ericengleman, plus Amazon.com's earnings call Thursday afternoon where this deal will certainly be a hot topic of discussion.

UPDATE: The WSJ's Deal Journal has more details on what motivated the Zappos board to go with a stock transaction versus a cash deal. Apparently the Zappos team thought Amazon's shares were undervalued at the time that dicussions began. The bet is paying off so far, with Amazon's stock gaining up more than 15 percent since mid-May.

Amazon's stock is surging again today, trading up more than five percent at about $93 per share. Given the 10 million Amazon shares that were used to purchase Zappos -- along with $40 million in cash -- the deal now is valued at roughly $970 million.

Could it top $1 billion by the end of this week?