I was referring to the runway length data and gross weight data when I
talked about easily available data. 4000 feet is a lot of runway for a
Bonanza.
 
Displaced thresholds are not relevant to takeoffs. You are expected to land
beyond them and are expected to start the takeoff at the beginning of the
runway and to use all of the displaced threshold.

Actually I did allow for the tailwind and forgot to mention it. I also used
max gross weight of 3600 pounds for the calculation. I suspect the aircraft
was several hundred pounds below gross. I can not speak to the slope, but
other comments in this thread suggested that the tailwind was accepted to
takeoff downhill. That would be normal procedure.

My point was that worst case analysis has him clearing a 50 foot obstacle at
least 500 feet before the end of the runway when the real obstacle was 500
feet beyond the end of the runway, lots of margin.