I think for your purpose..of taking in a reef, the goal is to take pressure off the main, so that you can ease the halyard and not have to fight the sail down. So, finding the right balance of rudder and jib is the key imo. If you have to harden up the mainsheet too much to hold your position, that kind of defeats the purpose. So in 25 knots, probaby a small jib would be enough. I have not sailed in SF Bay, but I understand the currents run strong. This is going to add an additional factor to your rudder positioning, depending on the strength and direction of the current vs the wind, you just have to play with it.
I don't know how the 31.1 behaves. I owned a 29 for many years. It tended to take a reef pretty early. I would have probably had 2 reefs by 25 knots. From what I read here about the SF Bay afternoon winds and have seen, I would probably have to leave the dock with at least one reef in 90 % of the time. Are the winds ever lite out there?
It seems like 15 to 25 is the norm.