Neither engine will be producing its rated output at cruise
speed. The actual power being produced at cruise
could be anywhere from 1/3 to 3/4 of maximum.
And different engines react differently to low-load running; many older design diesels are inefficient and may wear out faster if run at low load for a long time, while some modern computer-controlled diesels do very well at half throttle.
And a hull's resistance curve is usually far from linear, especially so when talking about displacement
or semi-displacement monohulls.
So it's not nearly as simple as "33% more power, 33% faster". Without a resistance curve for each boat and a set of performance graphs for each engine, any generalizations are vague at best.