I had a reply from the commodore if I remember suggesting that for the 34 a 4 meter one would be good. I have to admit to not having bought one yet but I am having my rigger visit me in a few weeks to assess how best to set up, ditto with a cruising chute.
I reached out to a number of manufacturers including Forespar in the States and the general advice was for a length between 4.0 to 5.4 meters, telescopic.
My hunch is that the ideal place to store would be on the mast given that Bavaria stanchions are not that robust and might struggle in bigger seas.
Sorry not to be more constructive but happy to chat further on the phone if you want to.