Thrash,
Once upon a time I had a twin DeHavilland Hornet with two Cyclon PC-4s on it. These are FAI/CL combat motors - not the fastest .15s as AKM, Fora, and others are faster, but they are plenty fast enough. They turn about 32,000 rpms at peak. They weigh four ounces each. The plane was way too fast.

At the Dixie Nats year before last Lee Liddle, 2004 National Champion, had a Messerschmidt ME-410 Hornisse with twin AKMs. It was at least 15 mph faster than anything in the air at the same time. We estimated it was running 110 mph. It could have gone much faster if he had props pitched for all out speed but he had it set for sustained speed in turns.

At the Paris, Texas Contest this year, Mike Willcox, former World Champion CL Combat flier put up a 72" span Falcon Flying Wing in Open B powered by an old Nelson .15 - it was undoubtedly the fastest plane at the event.

The Rossi may truly outperform them because it is a .21, not a size commonly used in airplanes, but then again the prop sizes necessary to fly the larger planes may give the upper hand to the .29 size engines like the FORA which is really a de-stroked US CL Combat .36.