Heavy arrows from a light bow will work as long as you are relatively close to the target. They tend to drop like rocks beyond 20 yards, but then that is exactly where I prefer my targets. My current setup is right at 11 grains per pound. The shoot pretty flat to about 22 yards, begin to drop at 25 and have a noticable arc at 30 and beyond. It's fun to shoot at foam from that distance, but I'd never shoot at a deer from beyond 25 yards.
The most important aspect is not arrow weight but arrow flight and placement. If you are getting good flight, no fishtailing, and you hit where you are looking, anything from about 8 grains per pound and up will work just fine.