RE: Heavy Carbons...
NYH, I went through similar thinking patterns a few months ago. What I did to test the theory out was to go to Walmart and buy one CE terminator hunter. I wouldn't want a dozen of them (poor specs) but it did tell me if my bow would be that much quieter for the speed I would be giving up. Funny thing was, it really didn't seem to shoot any quieter. So, I settled on ACCs, now have the same speed, but with top notch consistency.
If you play around in the ke programs, I think you'll find you might gain a few pounds of ke at best. A cheap way to test a theory...