The best approximation I’ve found is S&P has this Top 10 index[1]. Over the last 10 years it has performed 18% annually vs 11% for the overall S&P 500, but that’s obviously been a historic bull run in large cap growth stocks. I can’t find data going back to 2000 to see how that strategy would have played out, but curious if someone else finds it or crunches the numbers.

1. https://www.spglobal.com/spdji/en/indices/equity/sp-500-top-...