You need to define the extreme transients you desire protection from. If you can't do that, the rest of the exercise is pointless.
Youre bang on with that.
We'd love to be able to define them, but i reckon only those who have large scale access to the power networks of all countries in europe can really know what is the incidence rate, magnitude and duration of mains transients at any given mains outlet.
Even then i doubt anybody feels they really know.
I certainly have never seen a scoep shot of a mains transient, despite masses of google searching.
I dont hear of anybody doing a PhD in mains transients.
Only specific companies seem to know about mains transients, and it seems to me, that they keep this knowledge all to themselves....its their IP.