Why worry about so? Let the group size on the target tell you.
If you are talking 100 yard or 200 yard groups and are trying to build a load to shoot much longer distances, the group size won't necessarily tell the whole tale. A load with a high extreme velocity spread (or standard deviation if you chrono enough rounds to be valid as others have said) will start to exhibit vertical stringing at longer distances. That is not good. You already have to deal with estimating wind drift, throw in vertical dispersion on top of that and your probability of a first round hit drops even more.
For a rifle I don't plan on taking any shots over 4-500 yards with, I pay little attention to ES or SD if my 100 or 200 yd groups are small, so in that regard I agree with forpest. Just my 2 cents and worth every penny.
