well, i haven't sailed them both, but since there aren't many replies, i'll add my opinion.
i own a futura 111. my sense is that it sails a little big for 111 liters, and i doubt i would be using it with a 5.9..., maybe it will work for you if the water is really flat, like a lake or something...
I have used my futura 111 with a 6.5 (with the stock fin), and that's about as small a sail as i would use on the board. my conditions are typically somewhat bumpy when it's 6.5, and while the board was fast, it was sort of on the edge of control - in a fun way though. when it warms up here, i will try out a smaller fin for the 6.5.
I also have a 7.5 for the board, but haven't sailed that combo yet.