Thinking about buying my next board for local bump & jump conditions (17-25 kts), and wondering what minimum volume to go for?

Currently have a 10yr old 99L JP FreeMove and my weight is 78Kgs. My sails range from 4.7m - 6.5m, and generally prefer sailing above 18kts.

Just wondering if there is a commonly used volume for our local conditions stated above?

Is there a general rule of thumb: board volume = sailor weight + rig weight + X for the average sailor.

I think the board in that category would be around 85 litres is definitely the size you need