Ah, the ultimate question. Dealing with that very question myself this year. I was just reading an article on California Pinots and those who waited had mixed results. If you cant take the losses from the rain, it is better to pick than have nothing. We are in the same spot and I will probably pick right before the next rain. Rain plumps up the berries, but lowers the brix and accelerates rot. If they taste good (sweet and low acid bitterness) it might be time.