The lighter arrow looses KE faster than a heavier arrow. That is important at longer ranges. Just my opinion now, 60 yds is a bad shotat an elk with a bow and I know people do it. The KE is an issue at that range, but there is a bigger issue. That would be time of flight, an elk can move a long ways in a second.
Back to the issue, take those arrows out and shoot them at 80yds and see how well they fly. Mark you pin settings with the light arrows, then shoot the heavy ones and see which arrow really shoots better out of your bow.
Gselkhunter