Let's talk about that boat test between the Malango and the daydream, published 5 years ago by Voile and voiliers magazine. Have a look at the shape and both boat characteristics. They couldn't be more different in what regards shape hull even if the keels are similar
The boats have about the same weight, almost the same LWL, the Daydream compensates its inferior form stability with a bigger B/D ratio, the Daydeam has a much better prismatic coefficient and therefore needs less sail (power) for the same speed.
The theoretical hull speed for both boats is 7.08 for the Malango and 7.12 for the Daydream, a negligible difference of less than 0.04K.
The sea had no waves, or very small waves.
With 10k wind:
Close to the wind: Malango - 3.8K ....... Daydream - 3.9K
Downwind with Spinnaker : Malango -5.3K........ Daydream - 5.3k
(bigger one on the Malango)
With 20k wind:
Close to the wind: Malango - 5.7K ............ ....Daydream - 5.7K
Downwind with Spinnaker : Malango -8.2/surf 10K........Daydream - 8.2/surf 10k
(bigger one on the Malango)
Cruising speed: Malango - 4.8k ..........Daydream - 5.5k
Max speed: Malango - 7.1k ..........Daydream - 7.0k
Here the Malango had a 15hp yanmar and the Daydream a 19hp Volvo.
Regarding sailing those were at the time amazing results for me, results that now I can understand.
Assuming those two boats are optimized and very well designed, and I think they are this means:
That a narrow boat has an advantage upwind in weaker winds (I believe that with a 5K wind the difference would be much bigger) and that advantage can disappear in stronger winds, but for having the same performance the beamier boat has to carry more sail to overcome its superior prismatic coefficient. He can do that because that extra beam gives it a lot more hull stability and more power to carry more sail. However in weak and medium winds the narrow boat will heel less than the beamier boat.
That was not tested on that sail test, but comparative results taken from racing performance, indicates that these results are only valid on flat water. On stronger winds offshore you have waves and the wave drag of the narrow boat will be much smaller. On this situation (strong wind and waves) the narrow boat will be considerably faster and will pound a lot less.
Downwind you have a match here but I believe that if we were talking about 30k wind or more, the Malango would be considerably faster, being able to plan more easily. Not only more easily but with more control, with less lateral ballance (that big stern would have a damping effect).
Regarding the performance under engine I don't think that that 4hp difference is responsible for that big difference in cruising speed (we can see that the max speed is very close). The worse performance of very beamy sailboats under engine is a constant on this type of hull at half power. I guess that has a relation with its worse performance with light winds: That hull needs more power to be moved at slow speeds. At higher speeds, near hull speed and over the beamier hull can plan at lesser speed and makes less drag, the opposite than at slower speeds.
We are talking here about two almost extreme hull shapes, one very narrow and the other very beamy (and that's why I found amazing that the performance was so close). Those differences would be attenuated with a less narrow boat, giving different compromises, specially in what regards differences in planning and control downwind with stronger winds, heel of the boat, and induced drag on passing waves.