A good rule
of thumb for a displacement
hull is that it takes 15 hp per 10,000 lbs displacement
to push the boat to hull speed (the conventional 1.34 definition which may not apply to cats with their long, narrow hulls). With a Lagoon
380s cruising weight of 20,000 lbs and a lwl of 36, then that is 30 hp to push it to 8 kts.
30 out of 56/58 (the maximum output of two 3gms or 3YMs) is about as much as you want to pull out of those engines on a continuous basis.
To push it to 10-12 kts is going to take a lot more horsepower, probably more than the hull can stand.