I agree with the patterning thing. That's #1, along with knowing your gun's effective range. The Hevi-shot patterns far better in my gun--a Remington 870 Supermag with an Undertaker choke.

Hevi-shot will out-penetrate lead every time in any gun. If the pattern's equal---Hevi-shot is what you need.

Having said that----I've killed more turkeys with 2 3/4 #6 lead shot than any other shell.