I’ve driven by a few radar speed indicators in my car, and I’m consistently going 4 km/h less than what my digital speedometer says, regardless of speed. I find it difficult to believe this is an accident. So if I had your vehicle and it behaved like my speedometer does, I would still only be +1 over the limit. Also, I now drive with my speedometer +5 to +9 relative to the speed limit, which keeps me more in line with the traffic around me.