Going from an F225 to F250 might gain you about 3-4mph more in cruise and speed, but I believe in most boat tests the F250 burns more fuel then the F225, IMHO it is not worth 10k, but if speed is that big of a factor, maybe it is for your use. As for going to a 300 suzuki, you might get 5k as a trade in value, trade ins are never what the engine is really worth. You would do better selling it on your own and might get closer to 7-9k, not exact what they are selling for used. Going to a different brand will require all new controls, so whatever the 300zuke costs, add another grand+ to the cost. The 300 zuke might add about 5-7mph more in speed and might suit your need for speed better. I was going to recommend twin F150's, but the cruise is roughly the same with less fuel economy. To repower a perfectly good engine to gain speed would not be justification enough for me to repower, gaining maneuverability and safety of twins would add to that, but may not suit your want for more speed as well as your overall use of the boat. Compare numbers for a new 258 journey on Grady's website, it is basically the same hull as your boat. With the F350, the fuel drops off and you gain about 4mph at cruise. The 300 zuke fits in the middle of that engine and your current one. This will give you an idea of what you might expect of a 300zuke. Although the 300 zuke has been known to be fuel efficient, they are not as fast as some other brands so you may not gain as much speed as you would think.
IMHO it would be more economical to cruise at a higher rpm and use your current engine then it would be to spend upwards of 10k and gain maybe 3-4mph and still be burning more fuel since it is a bigger engine.
