Ferran, maybe you haven't read the first message.
Here is quantified example based on a typical curve Vf vs Vz.
You can easily place points C (best climb rate) and B (best climb angle), and It is clear to everyone that at point A the angle is less favorable than at point B.
However, you also know that to climb, you need the extra prop thrust corresponding to the "slope drag".
So, if you prefer to stay at full throttle in level flight, this supplement will produce an forward acceleration.
It is easy to calculate the slopes at A and B and the corresponding forward accelerations in level flight, since Acc. = g * Vz / Vf
At 58 km / h, in flight level, accéleration will 1.8 m / s2
At 75 km / h, in flight level, acceleration will 2.1 m / s2
So, to accelerate from 58 km/h to 75 km/h, you have to wait about 2.6 s, during which you will have traveled about 50 meters still at ground level
While climbing immediately at 58 km / h (< Vx), you would already be at a height of 2.6s x 3 = 8 meters.
A scale drawing will show you that
it is only above 60 meters (180 ft) that the Vx choice becomes interesting.
PS: With headwind, choosing A is even more interesting.