If you are currently planing with a Futura 122 and a 6.4 m2 sail how are you measuring the windspeed, and what is your weight.
Planing on a 6.5 m2 rig, in 10-12 knots is quite a feat.
You either must be very light weight, or the wind is really a bit more than 12 knots.
If you were currently planing with a 7.4 m2 in 12 knots, then yes, increasing the sail size between 0.5 and 1.0 m2 might allow you to plane in the same conditions with a Futura 111.
Figuring out what board and sail combination will plane in what windspeed with what sailor weight is not so easy.
Sailor skills, wind quality, fresh vs salt water, the type of sail are some of the other variables that make it difficult to predict what will plane in what windspeed with what size rig.
Hope this helps,