superrnova, I'm not sure how much experience you have with aircraft and more specifically the topic of measuring speed but you should be aware several diffrent numbers could all be correct.
Now if you know the difference between IAS, TAS, GS etc then you can just ignore this post from here on
I should say that I study this because I'm trying to become an ATCO, not a pilot, so a lot of people in here do know a LOT more on this than I. How ever I'm sure they will step in to clarify or correct me should I mess up somewhere.
The radar data will show a Ground Speed (it's based on the difference in position between two radar updates and calculated using that and the time lapsed). It gives you a number showing how far the aircraft travelled over the ground at that time.
The aircraft's instruments will show Indicated Airspeed (IAS). It shows the speed of which the aircraft moves through the air. The IAS varies with many things (such as winds for example). This means that it's many times not equal to the GS (shown on radar), at high levels the IAS and GS can differ by more than 100 knots.
I belive the FDR shows IAS (because it's a reading of the instruments) and the radars will show GS, so you might see different values here and you must also be aware about this difference when looking at speed limitations specified by the manufacturers.