>> S&P 500 is not the most popular US equities benchmark for pension funds. Russell is the preferred provider

> Where are you getting this from?

At least it seems correct for a subset that may or may not be representative: “This report intends to provide insights into the overall and asset class benchmarks selected by the 50 largest U.S. public defined benefit plans. [.. ] the Russell 3000 index was most frequently cited to measure U.S. equity performance.”

https://www.nasra.org/Files/Topical%20Reports/Investment/P&I...