Maybe if you provide a little more information - Weight, experience, typical conditions, sails, etc. others may jump in and help you out too.
My thought is that the futura 111 and 121 are too close in size and will overlap too much. I jump from my iS 111 to my formula board which works fine for me (8.4 on the iS to 9.2 on the formula). You need to think about your typical sailing conditions and if you could, what sails you would have in your quiver and then which boards would cover the range of conditions you will mostly encounter. In other words, estimate your perfect quiver of boards and sails, and as your skills improve and your money allows, add pieces to your quivers that make sense considering your overall goal. Both a futura 111 and 121 don't make sense.
Most windsurfers want to plane as early as possible, but many don't want to go with "giant sails and boards" because of the costs including masts and booms. With that said, most sailors that frequently encounter lighter winds (10-15 knots) will most likely have a sail in the 8-9 meter range and a large slalom or freeride board in the 130-140 liter range, then they may have one or two smaller boards for higher winds.
We are just guessing at what would work best for you until we get more information.
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.