Hi, I'm the same weight as you and I also like to jump ASAP on wave equipment, but as you can see in my signature, I have quite a collection of slalom equipment too. Else my TOW would be reduced to perhaps 20% of what I'm doing now.
First of all you need to decide about the border line between wave & salom. It is something personal.
Personally, I'm not interested in wave stuff when I need sails > 5.5 m2. Actually I only have 2 wave sails that I use frequently, i.e. 4.0 & 4.7 with 1 freewave board of 83L. I start using this equipment from +/- 22 knots and up to 40 knots. Below this I'm on slalom equipment. There are a few exceptions when the wind has the right direction for a few speed strips with dead flat water in my neighbourhood. Then I could also be on my IS87 with 5.7 and 6.7 in the same wind range 22 - 40 knots.
My 7.8 slalom (NP evo2) sail is probably my most used sail. I use it both on my IS122 and IS101, but mostly on the IS122. I almost always start using it on my IS122 and when I get too overpowered, I just switch the IS122 for the IS101 and the same 7.8 sail works again fine. For you the IS107 will be right in the sweetspot of the 7.8 sail.
The low end range will start from 13 knots average (bare minimum), below this you can forget to have fun.
The sweet spot wind range will be around 16-17 knots average, also depending on the water state.
The high end will be around 20 knots, unless you are an experienced PWA racer because those guys can hold on to this sail probably up to 25 knots and more.
Fin size for the IS107 will be around 40.
I heard that a carbon extender works fine on an X6 460 mast, but I've never tried it myself. It's probably not the most optimal. Anyway, If you also think about an 8.6 sail you should definitely also think about the new IS110. You will have a lot of fun in the 12-18 wind range with the 8.6 and in the 16-20 range with the 7.8.
I'm planning myself to replace the IS122 for the IS110.
Hope this helps.
IS87 / IS101 / IS122 / US147