I'm not surprised that this post might sit here awhile, not many people have experience using pistol powders in a rifle cartridge like the "Quieter Coyote Rifle" article did. I read the reloading threads in the Whisper section and everybody seems to be using the fast rifle powders even for subsonic.
Supressers are a good thing.
Not only do they save your ears but, in prone, they keep the dust out of your face. They are also flash suppressors in low light.