Electric Outboard Speed

I think you should read more, it is available online, you are missing the point.

Superconductor stacks are used instead of permanenet magnets in rotor, not as storage/battery, but compared to conductor coils, dissipation is reduced. Stator coils are also exchanged with supercondutive coils to reduce dissipation compared to conductor coils. In addition to increased efficiency, torque density is increased (i.e. motor size reduced for the same torque):


Superconductivity above room temperature is also not possible, the motor was build for the temperature range of 20K to 40K and tested at 30 K (-243 C), so I do not see how it could be done without cryogenics. And they call this high temperature superconductor (HTS) because it is not required to go close to absolute zero (-273 C), which would be even more complicated.

Battery/storage is independent topic. This team assumed that aircrafts start at first as hybrids with this motor and jet/turbine generator and then later as fully electric (i.e. on battery):

 

Bigger engine then!

 

This has become a bit off-topic, but you can only optimize the prop for one particular speed and thrust requirement.

So if you were to optimize for 3 knots, the energy requirement would be lower there, but unable to go faster efficiently at all, where a different propeller would use considerably more power at 3 knots but less at 5.

Generally the larger the diameter makes better efficiency and with a very high pitch to allow low rpm to achieve low speeds. Also choose a slender hull form. Keep in mind human power is about 120 watts and can easily achieve 11-12 knots at this amount of power carrying a human.

 

To me, this looks like the best answer for the OP (at the expense of weight).

From my experience with boats, in such cases, the time and money you spend for experiments and parts is equal to the money you need to add after selling the current one and buy new/used one which fits. Before deciding to proceed to experimenting, you need to question yourself the following questions: 1. Do you have a background knowledge?, 2. Do you at all want to learn this?, 3. Do you already have the tools required?, 4. In case you do not have tools, are you ready to invest in those tools and are these tools required only once or it will be used later or is it maybe possible to borrow tools?, 5. How much time is required for this?, 6. What is the price when all this summed up on top of the new propeller price?

In addition, the risk is that you could burn ESC, as stated by SolGato. In that case, you will either have to spend additional money to fix it (if possible) or throw it away (return to question 6 and check the calculation in this case).

In the end, it is 3 HP motor so the gain in coins is probably diminishing and only learning gains could be rewarding. In case of e.g. more than 20 HP, I think saving coins would make sense. Unless you are designing for serial production and optimzing every cent, but in that case you should probably contact motor manufacturer instead of forum.

 

For a light 10' boat, a higher pitch (e.g. 9") and slightly smaller diameter (e.g. 10") prop could help increase speed. However, boat shape, weight distribution, and drag are also factors limiting top speed. Experiment cautiously with prop sizes and your position in the boat to reduce turbulence and drag. Start with modest prop changes as major changes risk overloading the motor.
p.s. 1kW is not 1.3 hp. 1kW is 1.34102 mechanical horsepower or 1.3404 electrical horsepower.
https://www.asutpp.com/kw-to-hp.html