The original MPH speedometer was never very accurate, due to a worn inner spring that stopped the needle from tracking around correctly, and so have finally 'bitten the bullet' and installed a KPH unit, as reading speed would now be accurate plus require no interpretation on our kph-signed roads.
This speedometer is listed as being for a vehicle using 7.50x16 (235/85 r16) tires, while mine are 6.5, but having now driven a couple of times with the new speedo plus GPS to assess calibration, have found that under 60 kph the difference is barely noticeable (and with road vibration and bumps making the needle jiggle slightly, any difference virtually irrelevant). Above 60 kph the needle is reading about 6-7% higher than the GPS speed, but again with road vibration, plus the gauge location, plus parallax, making it hard to really tell - not to mention that at this speed one's eyes should be on the road!
But nice to have, and at a glance know pretty much at what speed I'm going without having to use the GPS.