I am not in a position to recommend you anything Razor...
I have neither a Patriot, nor a Jett 50 engine...
I just know that an 8x12 won't work on a plane like the Patriot...
Hell, even on the Magnum, which is a good deal sleeker and/or smaller, something more modest like an 8x10 doesn't even work...
But I think you're in the ball park with your 8.75x8 though.
The patriot is a sport plane after all, and was not really designed for extreme speeds, was it? So a little more diameter to get a little more thrust to overcome a little more drag might be the right way to go...