I've always used 6 because i was taught by my father that more hits are better, althought the 4's might pack a little more punch downrange i like have more chances to hit that head and neck. Turkey don't seem particularly tough if you hit them in the right spot so i would rather have more chances to hit that spot then more punch when it got there. I've killed a bird at 51 yards before with 6s (due to some poor range estimation in some open woods on my part, not a shot i would recommend) so i think their power is adequate at range. Really kind of a personal preference i suppose, also depends on what the gun likes.