I am trying to figure out how to calculate an average of the best five years
out of 8.

My first example is 0, 3, 3, 5, 5, 3, 5, 5 I would expect my average to be
4.6.

Another example is 5, -2, -2, -2, -2, 0, 0, 0 I would expect my average to
be -0.6