No worries on giving us a little more info to work with. More info here normally gets you better more informed responses.
If you are sailing a 6.0 m2 NP Solo at 75 Kg. (165.3 lbs.) on a large medium volume transition board now (One70 and Phoenix 320), and you are powered up most of the time, then a 122 liter board is not going to be a real problem for you to get used to.
The 111 liter will only be slightly more difficult.
Are all the other sailors where you have been sailing on 6.0 m2 rigs as well?
What size boards are sailors of height/weight similar to yours sailing?
It won't be as easy to uphaul the Futura 111 right at first, but the board has enough reserve volume for a 75 Kg. sailor to uphaul easily in flat water conditions.
When the conditions get rougher, and you can't uphaul, it's due to the water surface conditions, not the volume or width of your board.
So, take a look at what your friends and other sailors are using, and if you've got the skills mastered on the transiton boards (I hope you aren't using the centerboard to stay upwind) you should be able to adapt to the smaller Futura 111 or 122 very easily.
Rig size may be pretty critical here.
If you are using a 6.0 m2 on the big boards, you may want to look at a 6.5 -7.0 m2 rig for the smaller Futuras as you are going to need a little more power to get you going.
Hope this helps,