I went through the same decision process and got a +40 L board for learning to both wing and SUP.  The challenge is the shape as wing-only boards don't have to be shaped for paddling.  I was concerned the F-One would not paddle well.  I wasn't sure about Fanatic.  Seems heavy and I read some concerns about build quality.  I ended up going with a Jimmy Lewis Flying V (6-5, 115 L).   He makes 5 sizes.   I am 70 Kg.  I am very happy with my choice.  It has really progressed my winging and on non wind days, it is fun to practice paddling with foil attached for eventually getting into small waves (I am currently not a very good paddler).  The other boards I considered for dual use are Armstrong (3 sizes), Naish Hover and Kalama (very limited supply).  Good luck and let us know what you decide on.