In the case of which braodhead weight, you are not just supposed to choose which one. You want to choose the one that gets you more of a 10% front of center balance.

Put oneither grain head and balance the arrow close to the middle by resting the arrow on your finger. Mark that balance spot and mearsure the length from the front of the arrow to the center of the mark. Subtract that distance from half of your arrow length(in your case 13.5"). Then take that number and divide it by your arrow lenght(27"). Choose which ever grain head gets you closest to (.10). The two will be relatively close but one will be better. In my setup, the front of center distance is 2.6", and the front of center percentage is 2.6/27= (.097) or 9.7%.

I know this is a lot of math but this is the absolute engineering way of choosing a head correctly, not just choosing one on preference. The 10% front of center puts the arrows spine in the most optimal position during launch and flight and maximizes arrow flight stability.

I sort of bring my work philosophy to my bowhunting: "In GodWe Trust, all others bring data!!!!"