Ghengis,
It's interesting to see that you've made reference to gyro longstab. I've seen elsewhere in the web that several accidents have been attributed to PIO in these craft, and that airworthiness authorities are investigating the introduction of guidelines to address the issue.
I don't have the URL, but I suspect that it was the UK CAA?
I have only flown a vehicle of this type once....with an instructor. I didn't see any PIO tendencies at higher airspeed, although I was encouraged to fly with a "loose" grip on the stick.
I would be interesting to get a professional TPs opinion? (I know from the thread that we have some highly qualified ones here!)
Furthermore It would be interesting to see what engineering assessments have been made in this area, noting that this vehicle is mostly relegated to the recreational side of aviation.
Cheers
Wox