Reddit user /u/StopAndDecrypt posted the following chart, showcasing the speed of Block Propagation over the Bitcoin Network:

When blocks return to their maximum capacity, we will have normalized data for making better comparisons. StopAndDecrypt describes this as “an efficiency floor of 1-2 seconds and delay may no longer be the scaling bottleneck”.

This data has been retrieved from https://dsn.tm.kit.edu/bitcoin/.