Still haven't seen the CASA Final Report...
But, my inexperienced/low hours personal opinion is...
- From a Human Factors angle, they were in danger the instant his lady occupied a Front Seat.
The concern about OAT/ engine performance was a distraction that possibly over-occupied the owner's mind. Understood in marksmanship, the wind can affect the shooter, more-so than the projectile.
A Pilot (PM) in the RH seat would have noticed the airspeed, and "mentioned" it... and if the PF doesn't react properly & immediately.. take control.
- A CFI did that to me once... still have the Lesson embedded...and tinnitus.
Seriously, later when taught to spin a full aerobatic 'plane, I'd add a quick touch of aileron to deepen the inside wing's stall and positively establish the spin.
Just like he did, sadly.