Chrono's often will give different velocities on different days in different conditions.
You can drive yourself crazy comparing data from different conditions.
If you feel like you have a good load:
Shoot 5 shots at 500+ yards and check your vertical dispersion as you mentioned.
That will eliminate all doubt.
If you have 1" or less vertical , your velocity ES is good.
Even if you have a great group at 100yds you can still have 40fps ES.
I've shot .2" groups at 100yds and then shot at 600 and had 6" vertical.
Check out this link:
Ladder testing at 1k- Detailed article and video