Mr. B, you have accomplished great things with your Gemini, you know it well, and you obviously love your vessel, as all Captains should :-)
I've heard other owners also say that keeping the leeward board up is crucial to avoid flipping in heavy conditions, and caveats like this trouble me. I prefer hull stability to be a constant "given," not conditional upon adjustable configurations like centerboards. I'm too human, and I prefer it if the vessel sails better than I do every time.