Investors are still paying close to 50 times earnings for the top artificial intelligence stock.Nvidia (NVDA 1.20%) has been the ultimate growth stock to own over the past few years. Since 2021, its shares are up more than 700%. That would have been enough to turn a $15,000 investment in the stock back then into more than$120,000 today. And although it has been falling in recent weeks, it's still among the most valuable companies in the world.But there are always questions about its valuation, and whether ...