Detected speed is what showed on the radar, i.e. the speed you were actually doing assuming accuracy of equipment. Alleged is detected speed minus 2km/h if a cop and 3km/h if a camera, giving benefit of doubt which covers equipment inaccuracy and the odd chance your speedo is reading low...this is the speed that you get charged based on.
Speedos from factory are usually generous because the opposite creates law suits.
Therefore if alleged speed is a couple km over the limit, fair to say your speedo was probably displaying ~7-8km/h over the limit, unless you have recalibrated your speedo or changed your tyre circumference to a bigger size, which will make you as fast as or faster than what the speedo is actually displaying.
From what I hear most cops don't bother with 5km/h detected over / flamin mongrel fines. You would have to be picked on for them to get you for a couple km/h over. Cameras are a different story of course...