I did the following exercise with all my students
At altitude in the practice area, set up a full power climb at Vx. I then smoothly but fairly rapidly pulled the power back to idle to simulate an engine failure. The challenge was to get the airplane to a condition of best glide speed and normal rate of descent, usually about 600 ft min. Most students lost several hundred feet making the transition.
The take aways:
1) An immediate and significant pitch down is required or the airplane will very quickly enter a mushing stall with a huge rate of descent.
2) an initial pitch attitude significantly more nose down than what is the correct attitude to hold the normal glide speed is required in order for the aircraft to accelerate to a safe glide speed
3) The transition will take altitude so there is a no go zone where a power failure, while at Vx will result in a touchdown with a high rate of descent
The bottom line: Hold Vx only as long as you need to clear the obstacle and as quickly as possible accelerate to a higher speed and be prepared to apply an immediate large nose done pitch if the engine fails in the Vx climb.