Thanks for the replies !
So with Gepetto's advice BD seem to be the way to go
I've always been intrigued by P90's and the Supermassive descriptive just excited me ("From light crunch through to colossal fuzz tones, low notes stay sharp and focused ") but I'm a bit frightnened by the "massive bottom end" part...
What do you think of Black Dog bridge + Supermassive Neck for my G400 ?
Yeah, i'd probably be wary about using that neck pickup...... mostly because of the output (it's the same as the Black Dog bridge). Neck position is acoustically louder already, so you generally get a better match with something lower output. Not to mention when you adjust the pickup height - which you should always set to taste, or try to match in volume with the bridge pickup. With something of equal output to your bridge pickup you'd have a harder time matching the volumes together.
So I'm assuming you're looking for a humbucker sized P90 in the neck position - most any of the other ones around the 7k-ish range should suit you very well. As fate would have it, i actually this almost identical setup in a guitar already. Before i replaced the bridge pickup with the Black Dog, i had a set of Seymour Duncan Phat Cats in that guitar. Since i never used the neck pickup anyways, i left the PC neck pickup in while the Black Dog was in it. One day i just got curious and matched the neck pickup together with it volume-wise; it sounded killer.
I'm guessing something like the Nantucket/Blue Note would work great - though i'd certainly ask for Tim/Ben's input on a good HSP90 accompaniment, now you've settled on the BD bridge.