pimping a flying15

Provided you don't increase the righting moment with racks or trapezes, increasing the rig size would actually decrease the sideforce when fully powered up, as you'd have the same heeling moment generated by a smaller force with a longer (higher) lever arm!  You could actually increase the righting moment and then with a higher rig generate the same sideforce higher up.  But where would be the point?

I'd suggest that what you're looking for is a rig that generates more thrust for the given heeling moment, and that is a bit of an ask, given the highly developed state of the ff rig.  I am not convinced that the modern generation of fat headed rigs are so much more efficient compared to the pin-heads - the Fireball is startlingly fast to windward in a blow given its hull and available righting moment.

What would be nice would be a lighter, carbon mast, although the benefit on an ff would be limited given that they are best sailed upright.  But at least you might be able to flatten off the sail better, and it would spill more automatically in gusts, so you might, on average, get a bit more thrust.  Most likely the biggest gain would be in the ease of stepping the mast!

But whatever, you'd need a pretty well-sorted rig to beat the existing highly developed sails.  I wouldn't expect a mix up of mast from this boat and sails from another class to be much, if any improvement.

Now, if you're talking trapeze (surely a good idea on an ff?) we have a different scenario.

Edit: caveat: my remarks about sideforce are based on the fully-powered up situation. In less wind the boat will be quicker for sure with a bigger rig, but you wouldn't need to wait long before you got overpowered!  The extra speed would generate more lift off the foils too, so the keel should suffice, except maybe in manoeuvres when the speed was low - you need to sail for speed initially after tacks, but that's true of other, more modern boats with their minimal 'boards.