I can give you a "rule of thumb" formula that I use when rigging powerboats to illustrate to prospective owners why I suggest "horsepower X" based on "their" expectation of how they want the rig to perform.
What you will first need to do however, is estimate the actual rigged weight of the boat (including engine(s), gas, gear, batteries, passengers etc) - when it will be on the water under "normal" operating conditions.
That can be a little difficult on a hull that is not completed, but plans or working info can often give you a (possible) hull weight. To be safe add 10-15% to that and then estimate the rest (A 115 horse 4 stroke or DFI will weigh in at about 400 pounds etc).
So just for the purpose of an example the hull weight of the Bandido (according the the Glen-L site) is estimated to be 2700 lbs (wood version), add 800 pounds for motors, 200 pounds for batteries and other rigging (cables, controls, steering etc), upwards of 400 pounds for fuel (which may be conservative since a pair of 115's could burn 20+ gallons per hour at wide open throttle), and allow 500 pounds for passengers and their "junk for the day" = 4600 + 10% "just incase" = 5060 pounds "loaded" (which is close to fully loaded now since the displacement weight is on 5350)
So with a weight of 5060 pounds we can "estimate" how fast this rig would run with a pair of 115 horse outboards.
(I didn't create this math, most of it is based on theories from a math "dude" name Froude who came up with a bunch of hydrodynamic formula's - you can google him if you are really interested)
Anyhow, you divide the actual displacment (loaded weight) by the shaft horsepower of all motors =
5060/230 = 22 (this is called your power to weight ratio)
You then divide a "hull factor" (190 in the case of a high speed performance boat - (planing hulls have "hull factors" of between 150-190 and the number isn't static but using 150 for a runabout style hull and 190 for a bass boat/cigarette style hull is close enough)) by the square root of the power to weight ratio =
190/square root of 22 = 190/4.69 = 40.51 (estimated speed in Knots)
40.51 x 1.15 = 46.6 MPH is the theoretical top speed you could get with that hull/motor(s) combination IF the rig was operated at sea level, with an air temperature of 70 degrees and a relative humidity of 30% (ya I know
In "real life", if you reduce that "theoretical" speed by 10-15% (to account for atmospherics and less than "perfectly" tuned motor(s)) - you get a pretty good idea of how the rig will perform.
In this case, probably 40 mph would be a "reasonable" expectation.
I do have another formula that will tell "how many horses you need" if you want to achieve "X" speed, which is what I use far more often - most new boat owners have a speed in mind that they want to get and then rig from there.....
Yes, Plywood is "real" wood
A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it