Tested with prerelease Safari 14.0.1 and Chrome v.121. Tested on production 1.4GHz quad-core Intel Core i5-based 13-inch MacBook Pro systems with 8GB RAM, 256GB SSD, and prerelease macOS Big Sur.
Testing conducted by Apple in October 2020 by measuring page load performance of snapshot versions of 10 popular websites under simulated network conditions.