Monetary-wise bitcoin's already surpassed gold.

Longevity speaking though, that is a little hard to discern. Gold's been the standard of money ever since we learned how to count. It has value that we have already agreed upon and while it doesn't rise as fast as bitcoin, it's on a steady increase as the supply here on Earth dwindles. A case could be made for mining precious metals on nearby asteroids or whatever but that's a farfetched tale the way things are looking right now, and besides, it's not as if that will immediately dilute the value of gold anyway.

Bitcoin however, while fairly valued, is a little volatile for most people's tastes. This could deter them from investing, and not to mention the immutable supply which will only make it harder to get a hold of a bitcoin in the future.