So, I tested the 100% zebra's behaviour today very carefully, and noticed that:

- the moment it starts striping the sky depends on knee setting (I'm not clear if and how the gamma settings influence it),

- there *is* something like a scope wherein the zebra first appears; it's not as obvious as with the 70% setting, but opening the iris, you can reach a moment when it breefly appears and quickly disappears, with the sky brightness sort of falling down a bit; then - with further iris openig - zebras reappear there to stay for good, and only then the sky gets really blown out (i.e. loses any colour information - just white).

I guess the switch-off position in exposure and appearing/disappearing of zebras I described above is at the knee position, where the curve flattens.

Another important conclusion is that unless one is shooting against the sun, it is not the sky that gets blown out first; there may well be many other objects in the frame to do it easier, with the sky still retaining light blue colour. So, one must be careful to not overlook those tiny spots where zebra appears first, because if you increase exposure until the sky gets striped - it might already be too late to get a properly exposed picture, with patches of blown-out areas here and there (or just overall picture blandness).

Since active peaking (especially when set to medium or high) can obscure those tiny spots where zebra first appears, I can confirm that having them both on may not be optimal at all times.

I agree, I run with my hystogram on, very very helpful.