Where do I install my hairpin legs on this 8 foot long butcher block for my new workstation desk?
Yes to pilot holes. #10 or #12 pan head screws, 1-1/2&quot; long.
Subtleties in leg positioning aren't going to matter. If, as @FreeMan suggests, the desk has wobble problems, you could put two struts on the back legs that form triangles. Or you could tie it to a wall with a bracket if you had a wall handy.
For anyone facing the same questions about sag, the Sagulator, http://www.woodbin.com/calcs/sagulator/ is a great resource to see if a given piece of wood or wood product will sag under a particular design load. If the OP had a flimsier piece of wood, that might have guided the positioning of the legs or changed the design.