"Which is Faster, Scope or Irons", American Rifleman, July 1987, page 40. This article was not reprinted in the 1990 collection of NRA articles, Finn Aagaard on Hunting Rifles & Cartridges. I'm not sure it has been reprinted anywhere.The article was not reprinted in Wolfe Publishing "Selected Works" either. Aagaard had his son time him.shooting ghost ring, open and low powered scope. If I recall scope was quickest. If someone has that article it would answer the question.
When I set up my 416 Ruger for Cape Buffalo I had an NECG receiver sight and higher front sight as back up to my 1.75 x 6 Leupold. Not only was the scope faster but it was advantages to find clear shooting lanes in the thick brush of Tiger Bay while stalking buffalo. Perhaps with younger eyes a ghost ring sight would be quicker.