Ron. I am shooting 17.5 inch WWB custom arrows out of my Flatline at 465 grs about 445 FPS. I do think it is quieter than my Nitro 505 was. At least from my ears at the shot. There is a longer stroke. More power in the shot. Etc. But that 17.5 inch arrow shoots great and I've been using the shorter plastic stirrup the whole time and it doesn't hang way over etc.
Well good luck on your search.