Talen Energy has delivered a very large gain over the past three years, which puts a lot of weight on the question of whether its current share price of US$327.91 is properly supported by the sales it generates. With the stock also seeing some shorter term swings, investors are increasingly asking how much of that long run performance is backed by the company’s revenue base rather than shifting sentiment. Talen Energy has risen about 7x over the last three years, so a lot of future…