WW,

If you are looking for a very high horsepower engine, with an RPM advantage, it is going to cost you.

A Jett .90 is a clear candidate, able to spin a 12x6 (or an equivalent 11x8.5) at 14,700 RPM.

If you want to reduce your costs, you may be able to find a Rossi/Picco/OPS/YS .60-.65, from the beginning of the 80s, when F3A was limited to 10cc and RPM was in the 14-16K range. Some are offered in NIB condition, will definitely undercut the $335 asking price of the Jett and will be equipped with a full length pipe.

If you go for this possibility, you can get a 12K peaked engine, like the OS Hanno Special.

A 12x12 prop at 12K RPM is more HP and calculated pitch speed, than a Jett .90. It costs less too.

How fast do you want to go? This Patriot thing goes 120-125 mph, with a Rossi .53.