I've seen a bunch of Doug Nash boxes behind high winding SB engines over the years. Modified cars would shift at 9000 or 10,000 with no problem. But, I'm pretty sure those boxes had all been reworked and prepped by experts. The street 4+1 box couldn't be powershifted right out of the box. I don't know about the current Richmond 5 speed boxes but based on the little bit I've heard I don't think they are much better than the original Doug Nash boxes. I don't think Richmond ever changed the syncro design, at least they hadn't changed it a few years ago when I last looked into it.