Most studies have shown in the longer run the average speed in blanket 20s creeps back up to around 26-28MPH while average speed in 30s is 31. Most longer term studies have shown fatalities of pedestrians reduces quite a bit for the first 2-3 years but then returns to what it used to be in the longer run while cyclist fatalities generally doubles after a few years, probably due to a mixture of the lower limits slightly encouraging more people to cycle and the lower traffic limits making it harder for vehicles to pass cyclists, etc. resulting in more incidents.
Said this about cycling from the start.
My ebike goes 15mph.
No way to I want a car passing me at a delta of 5mph!
Thw amount of side by side time is too high. The gap for a car to wait to overtake St that speed is just too high.