You have to understand that even a 4x annual growth rate, at some point, will be unsustainable (think if/when the market cap hits $1T+).
I have been thinking about a better model these past few weeks/months, I see it more as a decaying trendline of growth, (and just to give a ballpark idea, I'm guessing the trendline decays at around 30% growth rate per year).
ie: If it was growing at 20x annual growth rate in year one, then in
year 2: 14x
year 3: 9.8x
year 4: 6.9x
year 5: 4.8x
year 6: 3.4x
etc