What's wrong with your C9.25 for the planets? That is a mighty fine instrument for them. A newtonain may be a step backwards as to get a gain in aperture you need a proportionately larger mount. You won't be coming out in front dollar wise in this way.
Have you attempted all the possiblities with your C9.25? Maybe you can ask in the solar system photo forum those wizards on how to get the most out of your existing gear. Larger isn't always better.
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