In my opinion the reason for more HP in any of the C Dorys. All of them will run up to about 30 mph with the "standard" hp--90 hp for the 22, and 150 for the 25. As Jody wisely notes, the 140 Suzuki is the same weight as the 115. (same block). Some of the 200's are the same weight as the 150's (Some outboards a smaller block 200 and a larger block 200 hp --and the weight will be more with the larger block.
If the boats are loaded down, they need more hp to achieve cruising speeds in the mid 20's--and sometimes that is the best speed to run.
I will make one comment on the 25 (I haven't seen many 25's with two 90's--more common to see the 26 with the two 90's from what I have observed. My first 2003 25 had the plywood in the tansom--only go as far as the sides of the splashwell--not all of the way across the transom as with many other brands. In view of this, when I was working on the cockpit and other issues, I put in two more layers of 1708 glass with epxoy-That boat has that much better distribution of the force of the motors across the transom. I am aware of several 22's with "over power", where the transom failed--it was not clear if there was rot in the transom. In at least one there was--so it would have failed at some point.
On my last 25 (2007--with a fiberglass interior), did not have the splash well laid right against the transom. There was a gap of about 3/8 of an inch between the transom and the transom part of the splashwell. It was pointed out to me, after i sold the boat--I had missed it--or it was not there?? But I felt obligated to correct that defect. It took me a few hours--which equals $$$ if you don't do the work yourself--to bore out the holes in the motor bolts (removing one at a time), and then making that solid glass from the back glass layer of the transom all of the way to the inner layer in the boat of the splash well. This basically was consentric circles of glass material in the transom, and then glass worked between the aft splashwell, about 1/4" thick, then the 3/8" void, and then the almost 2" thru the wooden part of the transom. When that one side was completed, the bolt hole redrilled, and tightened up Then the other side was done in an identical fashion. The wall of the splash well was crushed--and the top bolts holding the motor allowed the motor to be about 1/4" away from the transom. That boat already had a plate between the two bolts on the top and bottom. now it has larger plates, thicker alumium, and solid glass from the back (engine side) of the transom to the front laminate of the aft wall of the splash well.
If a higher hp motor would have been put on that boat, without checking and resolving this issue. it is possible to have a transom failure.
As noted the boats get squirley over 30 mph. So the extra HP is good for high altitude, and increased load. Not to give more speed. If you wanted more than 30 mph safely,, then there will have to be some significant modifications made to the boat's bottom. (such as truing the running surface, and putting skegs on.
