I certainly agree that you don't want your rudders to be too small! Otherwise you can literally spin out. My 5.0 rudders did not look bigger than the 5.8 rudders, but I could be wrong about that.

Rhino, as you know, the name of the game is to keep it wild the whole way downwind; the daggerboards are crucial to popping up the hull; how much the board should be down varies. My boat has much smaller boards than yours, and I only start pulling them up when it's above about 12kts.