Step Turn says in #731 above:
The Daily Mail states: "One of the cameras showed the aircraft was travelling at a 100knots while inverted at the top of the loop".
The apparent speed will depend on whether the cameraman was standing square on to the plane of the loop or at an inclined plane. i.e. it is next to impossible to give credence to this figure. (If the cameraman was standing in the plane of the loop, the apparent speed at the top would be nil).