Many investors use a valuation metric called a price-to-earnings (P/E) ratio. This popular metric is useful because it measures the stock price against a company's profits. And in Nvidia's case, its P/E ratio of 57 certainly looks expensive, considering it's roughly double the P/E ratio for the S&P 500.

Nvidia was the top S&P 500 stock performer in 2023 and led the benchmark index through much of this year. But no longer. Power generation firm Vistra skyrocketed in September to race past Nvidia stock.