ADS-B that you get off the web aviation tracking sites is GPS ground speed. And the data rate is spot values ever 3 seconds.
Its great and more than sufficient for controlled flight tracking and air traffic control. This crash investigation usage it is not very good.
Only thing I can comment is that it looks as if it was in one piece.
And for your information the max speed of the 737-800 at 10 000ft is 350 knots (650 km/h). Now you have to watch what the out put is of the flight radar stuff what units its in and its lateral ground speed so you would have to work out the angle with the rate of decent to get an approximate airspeed. Those numbers 550 looked hellish to me, how did the wings stay on, until I realised they were km/hr.