So I finally did a deliberate experiment on how fast you can walk down an IceCrete roadway (Concrete with Ice below it).
Starting from a stop, I walked over 800 blocks in 10 seconds. (I say 'over' because that was the point at which I fell off the roadway and kept flying forward for another 30 blocks.)
If we factor in acceleration, that comes up to a top speed of roughly 90 blocks per second.
Thaaaaaaaaaaaaaaaaaaaaaaaat's kinda ridiculous.