As suspected the change to move ordering to separate good captures from bad captures has already paid off. Moving bad captures to the bottom of the move order list made it trivial to skip bad captures in the quiescence search altogether. This is an idea I first read about in a discussion on r.g.c.c. between Bob Hyatt, Feng-Hsiung Hsu and others at https://groups.google.com/g/rec.games.chess.computer/c/H6XjY2L13eQ . Hyatt claimed a small improvement, though Hsu was skeptical. Time has proven Hyatt correct though; I believe this is something most strong programs do. In any event, it seems to be worth about 10 ELO for Prophet4 so it’s a keeper.