Thanks zoyd! Very interesting the fact that you had those same impressions and that finally you've changed your mind, I'll take it as a suggestion.
Actually I ended up in a Excel calculator posted somewhere in a thread. I played with it and I'm realizing that with BT1886 there's a strong relationship between contrast and the rate at which gamma goes up. So displays with very high contrast may show lower black levels (compared to pure power law) even at 10 IRE, or even 5 for best ones.
I will make other test in the following days, especially with my vpr Planar, I suspect that with a good display/projector, BT 1886 becomes very desirable.
Probably it's better getting rid of bad displays rather than BT1886....