Yeah Its a tough one, and all the measurements and sail combo's can do your head in.
However the 7m will work best with the F111, hands down, end of story. Off course you could use your 8 or 6, but the sweet spot is 7m. The new wider boards are just as quick, better bottom end, and hold speed better through lulls. Also in the chop they are just as comfy even with a little more width, they just sail of the tail a bit more. In 7m weather its certainly not an issue.
As for fin size its a personal choice, however anything from 36-42 will work, depending on what you like under foot.
Isonic 97 2013
JP Speed 50 2014
Severne Reflex 4 7.0,6.2,5.6