The Rossi 65 makes that claim at 17,000 rpm. That means about an 11" prop of maybe 7" of pitch to get the engine into it's power band (it might not even turn that big of prop). For instance, a racing quickie engine (Nelson or Jett) makes close to 3 hp at about 22K in the air. They are only turning 8 3/4" diameter with around 8 pitch, with very narrow blades. On a draggy airplane, you will not like the results. In many cases the better choice is the lower revving torquer with a big prop.