A little extra weight will not hurt in the open class. Yes, it will require a little more power to push but it will be more likely to finish.
The TP 56 series are a good choice as you can swing a decent size prop which helps with choppy race water.
I have a TP5670 motor in a 8S1P SGX rigger which runs around 72-75mph. I can also run it on 6S swinging gas size props.
However the TP 56 series are big compared to the standard 40mm motors. A lot will depend on how a motor fits in the hull. The JAE twin nitro hulls are pretty compact and may be challenging to fit large diameter motors.
You will need a decent 200A 8S ESC and that may be the hardest challenge.
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