Consider yourself lucky, you've found out sooner, rahter than later, that lots of people run oversized carbs. You might be able to crisp-up the throttle response with a 24mm carb, but I doubt that you'd gain anything power-wise. Getting the fuel curve dead-on would involve pilot jet, main jet, needle profile and needle jet changes...a major can of worms. Even if you gain 1-2mph of top speed, acceleration would be weaker at any speed below top end and the driveability, in all likelihood, would tend to suck.
A 22mm carb is enough to support well over 10-12hp, and the motor doesn't make that much in stock trim. For anything but a race bike, you'll be happier tuning for torque, which your engine will produce in abundance.