My figures are approx as follows - comparing with RA2:

True 30mph - Speedo reads 32mph

True 50mph - Speedo reads 53/54mph

True 70mph - Speedo reads 74/75mph

True 94mph - Speedo reads 100mph

So consistently roughly 6-7% overreading

The above figures match mine.( using gps)

Though I cannot confirm the one at 100mph !

Not enough private road to safely verify the top figure

i now cant test it as i have no gps now :(