My opinion is it's best to transplant before flowering. That being said, you can still transplant & won't lose much if any weight from your plants: the roots don't really keep growing in flower mode at the same rate. The new surrounding soil would just basically be a buffer zone for nutes & moisture, and make it easier to keep the pH stable by reducing the amount of salt buildup from the bottom of the pots touchin your roots. Personally I'd go with options 3 or 4, but any of them would be fine really since your plants are about half way through budding. If you leave them as is, I suggest a thorough flushing every other watering to keep nute lockout to a minimum.