I will be delighted to hear what others think, but putting Paparazzi based AP on such a jet sounds pretty risky to me. I assume there will be lots of vibrations due to jet engine, so you will need higher quality sensors for start. Also at this speed you might get easily out of the linear flight envelope during maneuvers (somebody who knows more about aerodynamics might correct me), so a simple PID control might not be sufficient in auto1/2 mode. Gain scheduling should help though.
Also I am not sure if the current AHRS algorithms can handle such velocities and accelerations.
Besides, if this plane looses control, it might be difficult to ever find it again...