Regarding the OBP-3 bass boost at 18dB, I think nobody has ever tried this as even with just a pinch of boost, it's already too much, so all the way up, it will destroy your speaker for sure. This preamp is known for being a kind of "too much of everything" and I can confirm.
I've played basses with the 3 above mentioned filter based preamps and my favourite has always been the Alembic approach which sounds more "natural" to me, but again it's a question of taste. I like the Wal preamp because, with the Wal pickups, it sounds massive and powerful. The ACG is certainly the most complete of all...