I've had mine to the 120 mark indicated. Not sure what the error ratio might be as speed increases but when Tom, Wendy , and I all went to the PA grand canyon Tom got me looking at those road side radar things and between 60 and 80 mph my speedo is dead on by the speed indicated on those.

I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!