Not to agree with everyone else, if you can shoot the heavier arrow as accurately as the light, choose the heavier. Before I went to South Africa this year, I wrestled with this very issue and choose to ignore numerous recommendations to shoot an arrow in excess of 600 grains. Instead, I chose to shoot the 540 grain gold tips that I used with my 52 lb. bw psa for whitetail. Now I did get a kudu, impala, and warthog, but I never got anymore than 7-8 inches of penetration on any animal and certainly no exit wound / pass throughs. With the same setup at the same distances (14 -17 yards), I always got atleast an exit wound and most times a pass through on deer and pigs. Not in africa. I've heard that african animals were tougher.... I really didn't believe it before. After tracking my impala which was double lunged for over 400 plus yards, I'm a believer. But as you already know, hit that heart and quartering away shots give you more wiggle room since the vitals on those animals are so far forward. My shot on the impala was a perfect broadside double lung shot that I would have been pleased with deer hunting. Now (and I mean in 2010 when I go back with heavier arrows) I'm probably going to pass on all shots not quartering away. Good luck and have a ball !