The Big Stik is not really a "high speed" plane... particularly because of it's thick wings and uncowled engine.

With the ST75 or OS75 it will unload in the air using a high pitch prop producing a good clip, but it is not blindingly fast.

Using the modeled OS75 in the sim, the plane will unload to the point the engine is running at 18000 RPM or so, something the specs say it can do, but we NEVER see in real life...

On the AV the Power Curve in the ST engine prevents the engine from reving over 140000 RPM even when unloaded, which more realistically reflects observed behaviour.