Welcome aboard, Slim. I sail a Catalina 22 in protected inland waters. I have a 7.5hp 4-stroke Honda which is more motor than I need for the 2500 lbs it pushes. A friend of mine uses the same motor on his C25 which weighs over 4000 lbs. The 7.5 hp motor is better suited to his boat than it is to mine.
Just based on that, I would say that for the SF Bay, you would want the 8hp motor for your boat. Maybe some of the SF Bay sailors on the Net could give you a better idea of what would be optimum for your situation.