It all depends on the hull, engine/prop size.
I know its not 5.5 bit I had a 1996 Northcraft 5.8m, twin Mariner 60's. Circa 32knts.
Didn't like them, made the boat feel lardy at the back end, fuel was eye watering too if you were pushing on a bit, something like 1.2 litres/mile. You are also double everything for servicing, it makes a difference.
Swapped them out for a single Suzuki df140, different boat, light, responsive and fuel consumption was far more acceptable, 0.8 litres/mile
There is a place on this planet for all of Gods creatures.........right next to my tatties and gravy.