Let me splane. I assume that the op was talking about getting a new 200 four stroke. You say you have a hpdi(2 stroke?). One of the first things I noticed when I went from the 225 2 stroke to 4 stroke was that they were geared different. The four stroke was turning more rpms for the same cruising speed.
The problem was, at wot the four stroke would only turn about 5300 rpms with a light load. As I understand it, the four should turn 5500-6000 with full load. I elected to go with a four blade 15" pitch that got me about 6100 with light load. It does seem a little under propped, but I would rather it turn a little free. Its got nothing to do with the mechanic.

Let me explain. First off the motor could have been losing carboration in one of the cylinders or a number of other mechanic issues. I will agree that the prop is the key to the equation. If someone were to ever tell their mechanic there boat was not planing at 3700 rpms, I hope that would be the first recommendation. But we're getting away from the topic.

No question you get more out of the hole with a two stroke vs a four stroke. I have a 2006 HPDI. Given my personal experience, you will get a boat that performs well (when proped correctly), no planning issues, is extremely fuel efficient and will get the job done.

Now if you want to enclose the transom and add a bracket, a 200 would be light.

And that is what is probably going to happen.enclosed transom and dual engine bracket.. Come to think about putting a single ,On a dual bracket , I believe you need a 30" shaft motor.. Yes, no??? My theory is it's.better to have more engine than not enough... But that just me... I like 2 strokes..

I want one of those motors that uses no fuel at 22kts. Guessing at 20-25 gallons fuel in a day is a wide spread. Actually, I can agree with your "guess" at 40 mph wot. My test was with little current or wind and checking my speed with two people, no gear and light load of fuel, I got 34 knots on the gps. Do the math, it works out to 39.126 mph. Real world estimating with more fuel, gear etc, I said 37-38 mph. Is that much different from your guess at 40.
I said that I may be a little under propped, but I was told long ago that having a motor spin more free will have it live longer. I would rather not have too much prop, which was the case with my 3blade 15-17.
If you notice, the wot is not much different than your motor. My four stroke lacks the torque at low end. I think that is why they changed the gear ratio to make up for it.
I'm still not sure what engine the op is buying. If he is buying a new inline 4 cylinder (2.8 liter), what does that have to do with your engine, hardcore.

I owned the same f225 on my 21 Paramount. I thought it would work out well but the first gen 225 were identical to the 200 except for the cowl sticker and price. At the time Yamaha utilized the industry fudge factor to pass a motor rated at 205 hp as either version of the f series. As far as the 200 hdpi goes.... It is over 100 lbs lighter than the F225 of that era and tested at the prop to 215 hp. I will also say the 200 hdpi was one if not the best hdpi of the series and absolutely apples and oranges compared to the f225.

Lol! Your hilarious, do you own a 23' with a 200? Don't be ignorant, my estimates are based on actual usage and OWNING the boat. A 5% delta?! Again, stop being an idiot.

A Paramount is a completely different hull design. I actually had a 21 Concept with a 200 Ocean Runner and the boat ran well but was not a speed demon. 200 HPDI is a great motor.

Here is a pretty fair comparison of the f150 vs the i4 f200. Not a whole lot of difference for adding 50 hp. Do you think the comparison would remain as relative when going from a 200 4 cyl to a 250 V6? I doubt it.

Agreed. My point is only to illustrate what is on the sticker is not what is always under the hood. Not all 200s are created equal by any stretch of the imagination.

From the test I posted above it appears the i4 f200 is another Yamaha ploy to sell with the sticker. That is why I feel the i4 f200 the OP is questioning is not enough motor for a 23 SC. The torque curve of a 4 stroke 4 cylinder is of no comparison to a direct injected V6 that is rated above it's cowl sticker... and torque is what a 23 foot offshore, deep V boat requires.... not a "200" hp 4 cyl motor that is at best marginally peppier than a 150 on the same boat and identical at cruise speed.

I agree. I don't think a light duty I-4, 4 stroke Yamaha 200hp is enough motor for the 23. Too weak and pretty heavy too (Compared to a 2 stroke)