Misho, I think your boards are too big overall. At just 72 kg the ideal size in 25 knots (steady) winds would be something like 80 liter and a 4.5 sail (or 5.5 - 6.0 if slalom sail). For your lake conditions you of course have to go a little bigger, with 30-35 plus liters you should be able to uphaul and float around in no wind at all. A board just over 100 liters should provide that for you.
I think you should look for a quiver like
Futura 101, at 65 cm wide relatively easy to uphaul, fast and easy to control at speed in chop (easier than iSonic)
iSonic 117 Wide for light winds (or even the 117 as your biggest slalom sails is a 8.4).
Formula with a 10 m2 fot really light winds.
On the other hand, you already have a JP Supersport 69 cm wide. I think you should start using this more... It is a really fast board, and should in most conditions be just as good as the iSonic 117 wide (and certainly good for 30 knots.
And the FSW 112 should also be good for 30 knots. You really should not need more than 3 boards (58 cm, 65 cm, 75-80 cm) and formula. And if you don't have a 80 liter board you should manage well with 2 boards (65 cm, 75-80 cm) + formula.
How should your 3 board quiver look like?