Locating data in a table

Using my posted example....Maybe this?

This formula returns the row ref for the first instance where the series
crosses 1000...either from below or above 1000.

F2: =MATCH(1,IF(E2<=1000,INDEX((E2:E4500<=1000)*(E3:E4501>=1000),0),
INDEX((E2:E4500>=1000)*(E3:E4501<=1000),0)),0)

Does that work for you?