Kicker size

[spring time]

I see e-tec is making a 15 high output saw it at the seattle boat show

 

[Foxsea]

I thought you were limited to 'hull speed' with a planing hull http://www.sailingusa.info/cal__hull_speed.htm no matter what size motor you used unless said motor can plane the boat.

You got that right!
A planing hull that's not planing is a displacement hull - a poor one, actually. My boat needs about 250 hp to get it on step but less than half that to stay there and cruise (thankfully!!! - the rate of doing work - hp - determines the rate of fuel consumption.) A kicker of 8hp or 50hp will never get it moving faster than displacement hull speed because it will not rise to plane without 250 hp. Basic hydrodynamics. 40 foot, heavy displacement hulls will easily run at hull speed with 80 h.p. The flawed notion is that a displacement hull can climb up and over its bow wave. Agreed, that a planing boat with enough horsepower will rise and may travel very quickly on the surface of the water. On a displacement boat the hull is immersed. The notion of climbing up and over the bow wave is unrealistic. More power drops the stern into the trough and increases the height of the bow wave. It’s like asking somebody to run instead of walk so the chin can pass the nose. As far as high thrust is concerned, tugs (displacement hulls) depend much more on developing very high thrust (Kort nozzles) than on sheer horsepower. BTW: Many seagoing vessels are single engine but that engine is very well maintained.

The 8 hp high thrust Yamaha kicker that I use will move my 25' planing hull at hull speed ~ 6 mph easily, even in wind and choppy water.