I honestly think a few pounds of gear more or less makes way less difference than wind strength or direction: a factor that can rarely be planned for if the goal is a certain distance in a day.

Some days you fly, some days you slog.

For me the biggest factor is getting up and away early in the morning, and getting lots of miles in before lunch break - especially if riding in hot weather. I typically wake up at 6 a.m and am on the road an hour later. I love the early morning hours