Your answer may depend on your sailing conditions. If you sail more in 15 - 25, then the smaller board is the answer. However, if most of your time is in the 10 - 20 range, the I would go with the 107.
I weigh 77 kg and have an iS 111 and it works great with my 6.6, 7.6 and 8.4 race sails. Since I rarely race slalom and I am freeriding, I go for a bump and jump board (see below) when the wind is over 20 knots for a smoother ride, plus I can chop hop which I can't do with the iS. Basically, the iS 111 is too much board over 18-20 knots for my weight.
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.