I KNOW I don't need all nine boards in my garage..

Maybe I need a smaller garage?
It also pays to remember that volume isn't the only consideration. It's only really relevant when you're wondering whether you'll float or not.
Width and shape are what we really need to compare when figuring out whether a board is suitable for the job in mind. Volume is a poor indicator.
As an example, I have a 220 litre bic Melody (old plastic longboard) and a 230 litre starboard Start. There's only 10 litres difference between them, but they are COMPLETELY different shapes, and have entirely different specialties.
You'll float on either board, so if you really have to choose then it comes down to the most common conditions and which board is most suitable most of the time.
Or, as has been suggested, just keep all of them (guilty!!) and get a new one as well.
Maybe it's easier to just figure out a better way to store them in order to make better use of the space in the garage!