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I voted O/R H. The prochamber and O/R H sound VERY SIMILAR. I was stuck between the two just as you are. So I kept searching and listening to every sound clip I could find and talked to everyone who has either combo as I could. I decided to go with the O/R H simply because I favored the sound just a tiny bit more. The O/R H sounded a little deeper when you revved it compared to the Prochamber. That was the deciding factor for me. But you can't go wrong with either one. As far as sound, they both get a 10/10 from me.