Quartz: Almost four months into 2015, Netflix is easily the best performing stock in America’s benchmark index. Buoyed by impressive growth in subscriber numbers and its continued international expansion, investors have bid Netflix shares up by more than 60 percent so far this year. Netflix is a volatile stock, so things can change quickly. But its rise — it’s now hurtling toward the $600 mark — is still hugely important for global content and media industries.