Hi Chris -
I had a Honda 8 on the 22, and have a Honda 15 on the 25 (both of them are the "classic" design). Never looked at the things side by side, but they are similar in size. Checking the Honda Marine web site shows they are (the new ones, anyway) essentially the same weight. I don't know how the Yamahas compare - to each other or the Hondas - because my computer virus protection prevents me from going to their web site.
(Sorry - that was just a joke to get old Red Fox riled up a little.)
I know in the Columbia River, which can have 5 knot current and a stiff wind at times, the 8 HP wasn't used much for trolling. Not enough authority to keep the boat straight and moving.
I also know this: Whichever motor you choose, if you clamp it directly on the transom of a CD 22, it will drag in the water when on plane. The transom angle is such that it will not tilt up enough, and it leaves the skeg and a good part of the prop kicking up the water.
To fix that, a few folks have put the motor on a fixed bracket; not necessarily to raise it up any higher, but to get the mounting board closer to vertical so all of the available swing in the tilt mechanism is used. It works great, although it might be harder to get a tie rod to work well between it and the main. But it does make for a little more room to steer it with the tiller handle.
Here is a layout sketch that can be used to make a custom bracket for the CD 22 transom that will get the mount hanging nearly straight up and down. If you can figure out what the drawing is supposed to mean, and have a sheet metal shop cut and bend a piece of 10 ga. (.120") stainless steel plate in that configuration, you'll give yourself a lot of options for hanging any old size kicker motor you want. After the bracket is all bent up, you can make a mounting board to bolt to it. Then using some c-clamps and a chunk of 2x4 to protect the inside of the transom, just clamp the thing on your boat and hang the motor on it to check the location before marking and drilling the holes.